Zirconia sintered body containing fluorescent agent

ABSTRACT

The present invention provides a zirconia sintered body containing a fluorescent agent and having excellent translucency and excellent strength. The present invention also provides a zirconia shaped body and a zirconia calcined body from which the zirconia sintered body can be obtained. The present invention relates to a zirconia sintered body comprising a fluorescent agent, wherein the zirconia sintered body comprises 4.5 to 9.0 mol % yttria, and has a crystal grain size of 180 nm or less, and a three-point flexural strength of 500 MPa or more. The present invention relates to a zirconia shaped body comprising a fluorescent agent, wherein the zirconia shaped body comprises 4.5 to 9.0 mol % yttria, and has a three-point flexural strength of 500 MPa or more after being sintered at 1,100° C. for 2 hours under ordinary pressure, and a crystal grain size of 180 nm or less after being sintered at 1,100° C. for 2 hours under ordinary pressure. The present invention relates to a zirconia calcined body comprising a fluorescent agent, wherein the zirconia calcined body comprises 4.5 to 9.0 mol % yttria, and has a three-point flexural strength of 500 MPa or more after being sintered at 1,100° C. for 2 hours under ordinary pressure, and a crystal grain size of 180 nm or less after being sintered at 1,100° C. for 2 hours under ordinary pressure.

TECHNICAL FIELD

The present invention relates to a zirconia sintered body containing afluorescent agent, among others.

BACKGROUND ART

A zirconia sintered body containing yttria has been used for dentalmaterials such as dental prostheses. Many of such dental prostheses areproduced by forming a zirconia shaped body of a desired shape, forexample, a disc or prism shape, through the process of pressing zirconiaparticles or shaping a slurry or a composition containing zirconiaparticles, followed by calcination of the zirconia shaped body into acalcined body (mill blank), and subsequent sintering of the zirconiacalcined body after cutting (milling) it into the shape of the desireddental prosthesis.

It is known that translucency improves when the yttria content in azirconia sintered body exceeds 4 mol % (see, for example, PatentLiterature 1). As a rule, improved translucency achieved by an increasedyttria content in such a relatively high content range often comes atthe expense of strength such as flexural strength. One possible way ofrelieving such strength decrease is to reduce the crystal grain size ofthe zirconia sintered body by, for example, using zirconia particles ofsmall particle size.

Incidentally, natural human teeth have fluorescence. This is problematicin dental prostheses because a dental prosthesis, when it is notfluorescent, appears as missing as it fails to fluoresce in anultraviolet environment, for example, such as in an amusement facilitylit with blacklights. One approach to overcoming this issue is to add afluorescent agent to the dental prosthesis. A zirconia sintered bodycontaining a fluorescent agent is known, for example, such as thatdescribed in Patent Literature 2.

CITATION LIST Patent Literature

-   Patent Literature 1: WO2015/098765-   Patent Literature 2: JP 2016-540772 T

SUMMARY OF INVENTION Technical Problem

In the course of investigations of the effect of adding a fluorescentagent to a zirconia sintered body exhibiting excellent translucency andstrength with an yttria content of 4.5 to 9.0 mol % and a crystal grainsize of 180 nm or less, the present inventors found that the strengthseriously decreases, and the translucency decreases way below theanticipated value when the fluorescent agent is simply added to thezirconia sintered body.

It is accordingly an object of the present invention to provide azirconia sintered body that excels in both translucency and strengthdespite containing a fluorescent agent. Another object of the presentinvention is to provide a zirconia shaped body and a zirconia calcinedbody from which such a zirconia sintered body can be obtained, andmethods for conveniently producing these.

Solution to Problem

The present inventors conducted intensive studies to achieve theforegoing objects, and found that a novel zirconia sintered body thatexcels in both translucency and strength despite containing afluorescent agent can be obtained by, for example, controlling the waythe fluorescent agent is mixed. It was also found that the novelzirconia sintered body is particularly preferred as, for example, dentalmaterials such as dental prostheses, and is highly useful not only as adental prosthesis used for the cervical region of a tooth but as adental prosthesis used for the occlusal surface of a posterior tooth,and the incisal region of a front tooth. The present inventors completedthe present invention after further studies based on these findings.

Specifically, the present invention relates to the following [1] to[29].

[1] A zirconia sintered body comprising a fluorescent agent, wherein thezirconia sintered body comprises 4.5 to 9.0 mol % yttria, and has acrystal grain size of 180 nm or less, and a three-point flexuralstrength of 500 MPa or more.[2] The zirconia sintered body according to [1], wherein the fluorescentagent contains a metallic element, and the zirconia sintered bodycomprises the fluorescent agent in an amount of 0.001 to 1 mass % interms of an oxide of the metallic element relative to a mass ofzirconia.[3] The zirconia sintered body according to [1] or [2], wherein thezirconia sintered body has a transmittance of 40% or more for light of700 nm wavelength through a thickness of 0.5 mm.[4] The zirconia sintered body according to any one of [1] to [3],wherein the zirconia sintered body comprises a cubical crystal as apredominant crystal phase.[5] The zirconia sintered body according to any one of [1] to [4],wherein the zirconia sintered body comprises a monoclinic crystal in afraction of 5% or less with respect to a tetragonal crystal and acubical crystal after being immersed in 180° C. hot water for 5 hours.[6] The zirconia sintered body according to any one of [1] to [5],wherein the zirconia sintered body is a dental material.[7] The zirconia sintered body according to [6], wherein the zirconiasintered body is a prosthesis for an occlusal surface of a posteriortooth, or a prosthesis for an incisal region of a front tooth.[8] A zirconia shaped body comprising a fluorescent agent, wherein thezirconia shaped body comprises 4.5 to 9.0 mol % yttria, and has athree-point flexural strength of 500 MPa or more after being sintered at1,100° C. for 2 hours under ordinary pressure, and a crystal grain sizeof 180 nm or less after being sintered at 1,100° C. for 2 hours underordinary pressure.[9] The zirconia shaped body according to [8], wherein the zirconiashaped body is formed from zirconia particles.[10] The zirconia shaped body according to [8] or [9], wherein thefluorescent agent comprises a metallic element, and the zirconia shapedbody comprises the fluorescent agent in an amount of 0.001 to 1 mass %in terms of an oxide of the metallic element relative to a mass ofzirconia.[11] The zirconia shaped body according to any one of [8] to [10],wherein the zirconia shaped body has a transmittance of 40% or more forlight of 700 nm wavelength through a thickness of 0.5 mm after beingsintered at 1,100° C. for 2 hours under ordinary pressure.[12] A zirconia calcined body comprising a fluorescent agent, whereinthe zirconia calcined body comprises 4.5 to 9.0 mol % yttria, and has athree-point flexural strength of 500 MPa or more after being sintered at1,100° C. for 2 hours under ordinary pressure, and a crystal grain sizeof 180 nm or less after being sintered at 1,100° C. for 2 hours underordinary pressure.[13] The zirconia calcined body according to [12], wherein the zirconiacalcined body is a product of calcination of a zirconia shaped bodyformed from zirconia particles.[14] The zirconia calcined body according to [12] or [13], wherein thefluorescent agent contains a metallic element, and the zirconia calcinedbody comprises the fluorescent agent in an amount of 0.001 to 1 mass %in terms of an oxide of the metallic element relative to a mass ofzirconia.[15] The zirconia calcined body according to any one of [12] to [14],wherein the zirconia calcined body has a transmittance of 40% or morefor light of 700 nm wavelength through a thickness of 0.5 mm after beingsintered at 1,100° C. for 2 hours under ordinary pressure.[16] A method for producing the zirconia shaped body of any one of [8]to [11], comprising a shaping step of shaping zirconia particles,wherein the zirconia particles comprise 4.5 to 9.0 mol % yttria, andhave an average primary particle diameter of 20 nm or less.[17] The method according to [16], wherein the method further comprisesa step of mixing a zirconia particle-containing slurry and aliquid-state fluorescent agent.[18] The method according to [16] or [17], wherein the shaping step is astep of slip casting a slurry comprising zirconia particles and afluorescent agent.[19] The method according to [16] or [17], wherein the shaping step is astep of gel casting a slurry comprising zirconia particles and afluorescent agent.[20] The method according to [16] or [17], wherein the shaping step is astep of pressing a powder comprising zirconia particles and afluorescent agent.[21] The method according to [16] or [17], wherein the shaping step is astep of shaping a composition comprising zirconia particles, afluorescent agent, and a resin.[22] The method according to [16] or [17], wherein the shaping step is astep of polymerizing a composition comprising zirconia particles, afluorescent agent, and a polymerizable monomer.[23] The method according to [22], wherein the shaping step is astereolithography process.[24] A method for producing the zirconia calcined body of any one of[12] to [15], comprising a step of calcining the zirconia shaped body ofany one of [8] to [11], or the zirconia shaped body obtained by themethod of any one of [16] to [23].[25] The method according to [24], wherein the calcination is carriedout between 300° C. or more and less than 900° C.[26] A method for producing the zirconia sintered body of any one of [1]to [7], comprising a step of sintering the zirconia shaped body of anyone of [8] to [11], or the zirconia shaped body obtained by the methodof any one of [16] to [23], under ordinary pressure.[27] The method according to [26], wherein the sintering is carried outbetween 900° C. or more and 1,200° C. or less.[28] A method for producing the zirconia sintered body of any one of [1]to [7], comprising sintering the zirconia calcined body of any one of[12] to [15], or the zirconia calcined body obtained by the method of[24] or [25], under ordinary pressure.[29] The method according to [28], wherein the sintering is carried outbetween 900° C. or more and 1,200° C. or less.

Advantageous Effects of Invention

According to the present invention, a zirconia sintered body is providedthat excels in both translucency and strength despite containing afluorescent agent. A zirconia shaped body and a zirconia calcined bodyare also provided from which such a zirconia sintered body can beobtained. The present invention also provides methods for convenientlyproducing these.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention is described below. It is to benoted that the following descriptions do not limit the presentinvention.

Zirconia Sintered Body

A zirconia sintered body of the present invention comprises afluorescent agent. By containing a fluorescent agent, the zirconiasintered body exhibits fluorescence. The type of fluorescent agent isnot particularly limited, and the fluorescent agent may be one or morefluorescent agents capable of emitting fluorescence under the light ofany wavelength. Examples of such fluorescent agents include thosecontaining metallic elements. Examples of the metallic elements includeGa, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent maycontain one of these metallic elements alone, or may contain two or moreof these metallic elements. For advantages such as enhancing the effectsof the present invention, the metallic elements are preferably Ga, Bi,Eu, Gd, and Tm, more preferably Bi and Eu. The fluorescent agent used toproduce the zirconia sintered body of the present invention may be, forexample, an oxide, hydroxide, acetate, or nitrate of the metallicelements above. The fluorescent agent may be, for example, Y₂SiO₅:Ce,Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, or BaMgAl₁₀O₁₇:Eu.

The content of the fluorescent agent in the zirconia sintered body isnot particularly limited, and may be appropriately adjusted according tosuch factors as the type of fluorescent agent, and the use of thezirconia sintered body. However, for advantages such as suitability asdental prostheses, the fluorescent agent content is preferably 0.001mass % or more, more preferably 0.005 mass % or more, even morepreferably 0.01 mass % or more, and is preferably 1 mass % or less, morepreferably 0.5 mass % or less, even more preferably 0.1 mass % or lessin terms of an oxide of the metallic element contained in thefluorescent agent, relative to the mass of the zirconia contained in thezirconia sintered body. With the fluorescent agent contained in anamount equal to or greater than these lower limits, the zirconiasintered body can produce fluorescence comparable to that of naturalhuman teeth. With the fluorescent agent contained in an amount equal toor less than the foregoing upper limits, decrease of translucency andstrength can be reduced.

The zirconia sintered body of the present invention may contain acolorant. By containing a colorant, the zirconia sintered body can havea color. The type of colorant is not particularly limited, and thecolorant may be a known pigment commonly used to color ceramics, or aknown dental liquid colorant. Examples of the colorant include colorantscontaining metallic elements, specifically, oxides, composite oxides,and salts containing metallic elements such as iron, vanadium,praseodymium, erbium, chromium, nickel, and manganese. The colorant maybe a commercially available colorant, for example, such as the PrettauColour Liquid manufactured by Zirkonzahn. The zirconia sintered body maycontain one kind of colorant, or may contain two or more kinds ofcolorants.

The content of the colorant in the zirconia sintered body is notparticularly limited, and may be appropriately adjusted according tosuch factors as the type of colorant, and the use of the zirconiasintered body. However, for advantages such as suitability as dentalprostheses, the colorant content is preferably 0.001 mass % or more,more preferably 0.005 mass % or more, even more preferably 0.01 mass %or more, and is preferably 5 mass % or less, more preferably 1 mass % orless, even more preferably 0.5 mass % or less, and may be 0.1 mass % orless, or 0.05 mass % or less in terms of an oxide of the metallicelement contained in the colorant, relative to the mass of the zirconiacontained in the zirconia sintered body.

With the present invention, a zirconia sintered body having excellenttranslucency can be obtained, despite that the zirconia sintered bodycontains a fluorescent agent. The zirconia sintered body of the presentinvention may contain a translucency adjuster for adjustment oftranslucency in the zirconia sintered body. Specific examples of thetranslucency adjuster include aluminum oxide, titanium oxide, silicondioxide, zircon, lithium silicate, and lithium disilicate. The zirconiasintered body may contain one kind of translucency adjuster, or maycontain two or more kinds of translucency adjusters.

The content of the translucency adjuster in the zirconia sintered bodyis not particularly limited, and may be appropriately adjusted accordingto such factors as the type of translucency adjuster, and the use of thezirconia sintered body. However, for advantages such as suitability asdental prostheses, the content of translucency adjuster is preferably0.1 mass % or less relative to the mass of the zirconia contained in thezirconia sintered body.

The zirconia sintered body of the present invention contains 4.5 to 9.0mol % yttria. The zirconia sintered body cannot have sufficienttranslucency with an yttria content of less than 4.5 mol %. The strengthdecreases when the yttria content in the zirconia sintered body is morethan 9.0 mol %. For advantages such as producing a zirconia sinteredbody having improved translucency and strength, the yttria content inthe zirconia sintered body is preferably 5.0 mol % or more, morepreferably 5.5 mol % or more, and is preferably 8.0 mol % or less, morepreferably 7.0 mol % or less. It is to be noted that the yttria contentin the zirconia sintered body is a fraction (mol %) of the number ofmoles of yttria with respect to the total number of moles of zirconiaand yttria.

The zirconia sintered body of the present invention has a crystal grainsize of 180 nm or less. Sufficient translucency cannot be obtained witha crystal grain size of more than 180 nm. For advantages such asproducing a zirconia sintered body having improved translucency, thecrystal grain size is preferably 140 nm or less, more preferably 120 nmor less, even more preferably 115 nm or less, and may be 110 nm or less.The lower limit of crystal grain size is not particularly limited, andthe crystal grain size may be, for example, 50 nm or more, or 100 nm ormore. The crystal grain size of the zirconia sintered body can bedetermined by taking a micrograph of zirconia sintered body crosssections with a field emission scanning electron microscope (FE-SEM),and finding a mean value of diameters of circles corresponding to 10arbitrarily selected particles from the micrograph (the diameters oftrue circles having the same areas as these particles).

The zirconia sintered body of the present invention excels in strength,despite containing a fluorescent agent. The zirconia sintered body ofthe present invention has a three-point flexural strength of 500 MPa ormore, preferably 600 MPa or more, more preferably 650 MPa or more, evenmore preferably 700 MPa or more, particularly preferably 800 MPa ormore. With the three-point flexural strength falling in these ranges,the zirconia sintered body of the present invention can have a reducedchance of breaking or fracturing in the mouth when used as, for example,a dental prosthesis. The upper limit of three-point flexural strength isnot particularly limited, and the three-point flexural strength may be,for example, 1,500 MPa or less, or 1,000 MPa or less. The three-pointflexural strength of zirconia sintered body can be measured incompliance with JIS R 1601:2008.

The zirconia sintered body of the present invention excels intranslucency, despite containing a fluorescent agent. The zirconiasintered body of the present invention has a transmittance of preferably40% or more, more preferably 45% or more, and may have a transmittanceof 46% or more, 48% or more, 50% or more, or 52% or more for light of700 nm wavelength through a thickness of 0.5 mm. With the transmittancefalling in these ranges, the zirconia sintered body can more easilysatisfy the level of translucency required for the incisal region whenused as, for example, a dental prosthesis. The upper limit oftransmittance is not particularly limited, and the transmittance may be,for example, 60% or less, or 57% or less. The transmittance of zirconiasintered body for light of 700 nm wavelength through a thickness of 0.5mm may be measured with a spectrophotometer. For example, thetransmittance can be measured with an integrating sphere by measuringlight from a light source passing and scattering on a specimen, using aspectrophotometer (Hitachi spectrophotometer, Model U-3900H manufacturedby Hitachi High-Technologies Corporation). In the measurement, thetransmittance for light of 700 nm wavelength may be determined aftermeasuring transmittance in a wavelength region of 300 to 750 nm. Thespecimen used for measurement may be a disc-shaped zirconia sinteredbody having mirror polished surfaces and measuring 15 mm in diameter and0.5 mm in thickness.

The predominant crystal phase of the zirconia sintered body of thepresent invention may be a tetragonal crystal or a cubical crystal.However, the predominant crystal phase is preferably a cubical crystal.The zirconia sintered body of the present invention is preferably atleast 50% cubical crystal, more preferably at least 70% cubical crystal.The fraction of the cubical crystal in the zirconia sintered body may bedetermined by crystal phase analysis. Specifically, the fraction ofcubical crystal may be determined by X-ray diffraction (XRD) analysis ofa mirror finished surface portion of the zirconia sintered body, usingthe following formula.

f _(c)=100×I _(c)/(I _(m) +I _(t) +I _(c))

Here, f_(c) represents the fraction (%) of the cubical crystal in thezirconia sintered body, I_(m) represents the height of a peak (a peakattributed to the (11-1) plane of a monoclinic crystal) near 2θ=28degrees, I_(t) represents the height of a peak (a peak attributed to the(111) plane of a tetragonal crystal) near 2θ=30 degrees, and I_(c)represents the height of a peak (a peak attributed to the (111) plane ofthe cubical crystal) near 2θ=30 degrees. When the peak near 2θ=30degrees appears as a peak attributed to a mixed phase of the (111) planeof the tetragonal crystal and the (111) plane of the cubical crystal,and separation is difficult to achieve for the peak attributed to the(111) plane of the tetragonal crystal and the peak attributed to the(111) plane of the cubical crystal, I_(t) and I_(c) can be determined byfirst determining the ratio of tetragonal crystal and cubical crystalusing a technique such as the Rietveld method, and then multiplying theratio by the height (I_(t+c)) of the peak attributed to the mixed phase.

In the zirconia sintered body of the present invention, the fraction ofmonocinic crystal with respect to tetragonal crystal and cubical crystalafter the zirconia sintered body is immersed in 180° C. hot water for 5hours is preferably 5% or less, more preferably 3% or less, even morepreferably 1% or less. With the fraction falling in these ranges, volumechanges due to aging can be reduced, and breakage can be prevented whenthe zirconia sintered body is used as, for example, a dental prosthesis.The fraction can be determined by mirror polishing a surface of thezirconia sintered body, and measuring the mirror polished surfaceportion by X-ray diffraction (XRD) analysis after the zirconia sinteredbody is immersed in 180° C. hot water for 5 hours, using the followingformula.

f _(m)=100×I _(m)/(I _(t+c))

Here, f_(m) represents the fraction (%) of the monocinic crystal withrespect to the tetragonal crystal and the cubical crystal in thezirconia sintered body immersed in 180° C. hot water for 5 hours, I_(m)represents the height of a peak (a peak attributed to the (11-1) planeof the monoclinic crystal) near 2θ=28 degrees, and I_(t+c) representsthe height of a peak (a peak attributed to a mixed phase of the (111)plane of the tetragonal crystal and the (111) plane of the cubicalcrystal) near 2θ=30 degrees. When I_(t+c) cannot be easily specified asa result of the peak near 2θ=30 degrees separately appearing as a peakattributed to the (111) plane of the tetragonal crystal and a peakattributed to the (111) plane of the cubical crystal, I_(t+c) can bedetermined as the sum of the height (I_(t)) of the peak attributed tothe (111) plane of the tetragonal crystal and the height (I_(c)) of thepeak attributed to the (111) plane of the cubical crystal.

The method of production of the zirconia sintered body of the presentinvention is not particularly limited, and the zirconia sintered bodymay be produced by, for example, sintering a fluorescent agent- and 4.5to 9.0 mol % yttria-containing zirconia shaped body under ordinarypressure. The zirconia sintered body of the present invention also maybe produced by calcining such a zirconia shaped body, and sintering theresulting zirconia calcined body containing a fluorescent agent and 4.5to 9.0 mol % yttria under ordinary pressure. The present inventionencompasses a zirconia shaped body containing a fluorescent agent and4.5 to 9.0 mol % yttria, and that has a three-point flexural strength of500 MPa or more after being sintered at 1,100° C. for 2 hours underordinary pressure, and a crystal grain size of 180 nm or less afterbeing sintered at 1,100° C. for 2 hours under ordinary pressure; and azirconia calcined body containing a fluorescent agent and 4.5 to 9.0 mol% yttria, and that has a three-point flexural strength of 500 MPa ormore after being sintered at 1,100° C. for 2 hours under ordinarypressure, and a crystal grain size of 180 nm or less after beingsintered at 1,100° C. for 2 hours under ordinary pressure. The zirconiasintered body of the present invention having excellent translucency andexcellent strength despite containing a fluorescent agent can beproduced with ease from such a zirconia shaped body and zirconiacalcined body.

Zirconia Shaped Body

The zirconia shaped body of the present invention comprises afluorescent agent and 4.5 to 9.0 mol % yttria, and has a three-pointflexural strength of 500 MPa or more after being sintered at 1,100° C.for 2 hours under ordinary pressure, and a crystal grain size of 180 nmor less after being sintered at 1,100° C. for 2 hours under ordinarypressure. The zirconia shaped body of the present invention can beformed from zirconia particles.

The fluorescent agent contained in the zirconia shaped body of thepresent invention may be the same fluorescent agent contained in thezirconia sintered body to be produced. The content of the fluorescentagent in the zirconia shaped body may be appropriately adjustedaccording to, for example, the content of the fluorescent agent in thezirconia sintered body to be produced. Specifically, the content of thefluorescent agent in the zirconia shaped body is preferably 0.001 mass %or more, more preferably 0.005 mass % or more, even more preferably 0.01mass % or more, and is preferably 1 mass % or less, more preferably 0.5mass % or less, even more preferably 0.1 mass % or less in terms of anoxide of the metallic element contained in the fluorescent agent,relative to the mass of the zirconia contained in the zirconia shapedbody.

When producing a zirconia sintered body containing a colorant, it ispreferable that the colorant be contained in the zirconia shaped body.The content of the colorant in the zirconia shaped body may beappropriately adjusted according to, for example, the content of thecolorant in the zirconia sintered body to be produced. Specifically, thecontent of the colorant in the zirconia shaped body is preferably 0.001mass % or more, more preferably 0.005 mass % or more, even morepreferably 0.01 mass % or more, and is preferably 5 mass % or less, morepreferably 1 mass % or less, even more preferably 0.5 mass % or less,and may be 0.1 mass % or less, or 0.05 mass % or less in terms of anoxide of the metallic element contained in the colorant, relative to themass of the zirconia contained in the zirconia shaped body.

When producing a zirconia sintered body containing a translucencyadjuster, it is preferable that the translucency adjuster be containedin the zirconia shaped body. The content of the translucency adjuster inthe zirconia shaped body may be appropriately adjusted according to, forexample, the content of the translucency adjuster in the zirconiasintered body to be produced. Specifically, the content of thetranslucency adjuster in the zirconia shaped body is preferably 0.1 mass% or less relative to the mass of the zirconia contained in the zirconiashaped body.

The yttria content in the zirconia shaped body of the present inventionmay be the same as the yttria content in the zirconia sintered body tobe produced. Specifically, the yttria content in the zirconia shapedbody is 4.5 mol % or more, preferably 5.0 mol % or more, more preferably5.5 mol % or more, and is 9.0 mol % or less, preferably 8.0 mol % orless, more preferably 7.0 mol % or less. It is to be noted that theyttria content in the zirconia shaped body is a fraction (mol %) of thenumber of moles of yttria with respect to the total number of moles ofzirconia and yttria.

The density of the zirconia shaped body is not particularly limited, andvaries with factors such as the method of production of the zirconiashaped body. However, for advantages such as producing a more compactzirconia sintered body, the density is preferably 3.0 g/cm³ or more,more preferably 3.2 g/cm³ or more, even more preferably 3.4 g/cm³ ormore. The upper limit of density is not particularly limited, and maybe, for example, 6.0 g/cm³ or less, or 5.8 g/cm³ or less.

The shape of the zirconia shaped body is not particularly limited, andmay be chosen as desired according to use. However, for example,considering ease of handing of when producing a zirconia calcined bodyto be used as a mill blank for producing a dental material such as adental prosthesis, the zirconia shaped body preferably has a disc or aprism shape (e.g., rectangular). By using a technique such asstereolithography, a shape corresponding to the shape desired for theproduct zirconia sintered body can be imparted to the zirconia shapedbody during its production, as will be described later. The presentinvention also encompasses zirconia shaped bodies having such desiredshapes. The zirconia shaped body may have a monolayer structure or amultilayer structure. With a multilayered zirconia shaped body, theresulting zirconia sintered body can have a multilayer structure, whichallows translucency and other physical properties to be locally altered.

For considerations such as ease of handling, the zirconia shaped bodyhas a biaxial flexural strength in a range of preferably 2 to 10 MPa,more preferably 5 to 8 MPa. The biaxial flexural strength of zirconiashaped body can be measured in compliance with JIS T 6526:2012.

The zirconia shaped body of the present invention has a crystal grainsize of 180 nm or less after being sintered at 1,100° C. for 2 hoursunder ordinary pressure (after the zirconia shaped body is formed into azirconia sintered body; the sintering performed under these conditionsmay be preceded by calcination at 700° C. for 2 hours under ordinarypressure). In this way, the zirconia sintered body of the presentinvention having excellent translucency can be produced with ease. Foradvantages such as producing a zirconia sintered body having even highertranslucency, the crystal grain size is preferably 140 nm or less, morepreferably 120 nm or less, even more preferably 115 nm or less, and maybe 110 nm or less. The lower limit of crystal grain size is notparticularly limited, and the crystal grain size may be, for example, 50nm or more, or 100 nm or more. Here, the crystal grain size is ameasured value obtained in the same manner as in the crystal grain sizemeasurement described above in conjunction with the zirconia sinteredbody.

The zirconia shaped body of the present invention has a three-pointflexural strength of 500 MPa or more after being sintered at 1,100° C.for 2 hours under ordinary pressure (after the zirconia shaped body isformed into a zirconia sintered body; the sintering performed underthese conditions may be preceded by calcination at 700° C. for 2 hoursunder ordinary pressure). In this way, the zirconia sintered body of thepresent invention having excellent strength can be produced with ease.For advantages such as producing a zirconia sintered body having evenhigher strength, the three-point flexural strength is preferably 600 MPaor more, more preferably 650 MPa or more, even more preferably 700 MPaor more, particularly preferably 800 MPa or more. The upper limit ofthree-point flexural strength is not particularly limited, and thethree-point flexural strength may be, for example, 1,500 MPa or less, or1,000 MPa or less. Here, the three-point flexural strength is a measuredvalue obtained in the same manner as in the three-point flexuralstrength measurement described above in conjunction with the zirconiasintered body.

The zirconia shaped body has a transmittance of preferably 40% or morefor light of 700 nm wavelength through a thickness of 0.5 mm after beingsintered at 1,100° C. for 2 hours under ordinary pressure (after thezirconia shaped body is formed into a zirconia sintered body; thesintering performed under these conditions may be preceded bycalcination at 700° C. for 2 hours under ordinary pressure). In thisway, the zirconia sintered body of the present invention havingexcellent transparency can be produced with ease. For advantages such asproducing a zirconia sintered body having even higher translucency, thetransmittance is more preferably 45% or more, and may be 46% or more,48% or more, 50% or more, or 52% or more. The upper limit oftransmittance is not particularly limited, and the transmittance may be,for example, 60% or less, or 57% or less. Here, the transmittance is ameasured value obtained in the same manner as in the measurement oftransmittance for light of 700 nm wavelength through a thickness of 0.5mm described above in conjunction with the zirconia sintered body.

Method of Production of Zirconia Shaped Body

The method of production of the zirconia shaped body of the presentinvention is not particularly limited. However, for easy production ofthe zirconia sintered body of the present invention that excels in bothtranslucency and strength, it is preferable that the zirconia shapedbody be produced by a method that includes a shaping step of shapingzirconia particles, more preferably a method that includes a shapingstep of shaping zirconia particles in the presence of a fluorescentagent.

The yttria content in the zirconia particles used is preferably the sameas the yttria content in the zirconia shaped body, and, in turn, theyttria content in the zirconia calcined body and the zirconia sinteredbody to be produced. Specifically, the yttria content in the zirconiaparticles is preferably 4.5 mol % or more, more preferably 5.0 mol % ormore, even more preferably 5.5 mol % or more, and is preferably 9.0 mol% or less, more preferably 8.0 mol % or less, even more preferably 7.0mol % or less. It is to be noted that the yttria content in the zirconiaparticles is a fraction (mol %) of the number of moles of yttria withrespect to the total number of moles of zirconia and yttria.

The zirconia particles used have an average primary particle diameter ofpreferably 30 nm or less. In this way, the zirconia shaped body of thepresent invention, and, in turn, the zirconia calcined body and thezirconia sintered body of the present invention can be obtained withease. For considerations such as ease of production of the zirconiashaped body of the present invention, and, in turn, the zirconiacalcined body and the zirconia sintered body of the present invention,the average primary particle diameter of the zirconia particles is morepreferably 20 nm or less, even more preferably 15 nm or less, and may be10 nm or less, and is preferably 1 nm or more, more preferably 5 nm ormore. The average primary particle diameter of zirconia particles can bedetermined by, for example, taking a micrograph of zirconia particles(primary particles) with a transmission electron microscope (TEM), andfinding a mean value of particle diameters (maximum diameters) measuredfor arbitrarily chosen 100 particles from the photographed image.

For considerations such as ease of production of the zirconia shapedbody of the present invention, and, in turn, the zirconia calcined bodyand the zirconia sintered body of the present invention, it ispreferable that the zirconia particles contain primary particles of 50nm or more in an amount of preferably 5 mass % or less, more preferably3 mass % or less, even more preferably 1 mass % or less. The content canbe measured by using, for example, a zeta potential meter.

The method of preparation of zirconia particles is not particularlylimited, and the zirconia particles may be prepared by using, forexample, a breakdown process that pulverizes coarse particles into afine powder, or a building-up process that synthesizes particles throughnucleation and nuclear growth from atoms and ions. The building-upprocess is more preferred for obtaining high-purity, fine zirconiaparticles.

The breakdown process may use, for example, a ball mill or bead mill forpulverization. Here, it is preferable to use microsize pulverizationmedia, for example, pulverization media of 100 m or less. Preferably,the pulverization is followed by classification.

The building-up process may be, for example, vapor-phase pyrolysis,which is a process by which an oxoacid salt of high-vapor-pressure metalions, or a high-vapor-pressure organometallic compound is decomposedunder heat through vaporization to precipitate an oxide; vapor-phasereaction, which synthesizes particles through vapor-phase chemicalreaction of a high-vapor-pressure metallic compound gas with a reactivegas; evaporative concentration, in which a feedstock material is heatedto evaporate, and cooled rapidly in an inert gas of a predeterminedpressure to condense the steam into a fine particle form; a melt processthat forms a powder by cooling and solidifying small liquid droplets ofmelt; solvent evaporation, which causes precipitation in asupersaturated state created by increasing the concentration byevaporating the solvent in a solution; or a precipitation process inwhich the solute concentration is brought to a supersaturated statethrough reaction with a precipitating agent or hydrolysis, and a poorlysoluble compound such as an oxide and hydroxide is precipitated throughnucleation and nuclear growth.

The precipitation process can be sub-divided into processes thatinclude: homogenous precipitation in which a precipitating agent isgenerated in a solution by chemical reaction to eliminate localheterogeneity in the concentration of precipitating agent;coprecipitation in which a plurality of metal ions coexisting in asolution is simultaneously precipitated by addition of a precipitatingagent; a hydrolysis process that produces an oxide or hydroxide throughhydrolysis from a metal salt solution, an alcohol solution of metalalkoxide or the like; and solvothermal synthesis that produces an oxideor hydroxide from a high-temperature high-pressure fluid. Thesolvothermal synthesis is further divided into processes that includehydrothermal synthesis that uses water as solvent, and supercriticalsynthesis that uses a supercritical fluid such as water or carbondioxide as solvent.

Regardless of the building-up process, it is preferable to increase theprecipitation rate to obtain finer zirconia particles. Preferably, thezirconia particles produced are classified.

The zirconium source in the building-up process may be, for example,nitrate, acetate, chloride, or alkoxide. Specifically, for example,zirconium oxychloride, zirconium acetate, and zirconyl nitrate may beused.

In order to achieve the foregoing yttria content ranges in the zirconiaparticles, yttria may be added in the process of producing zirconiaparticles. For example, a solid solution of yttria may be formed inzirconia particles. The yttrium source may be, for example, nitrate,acetate, chloride, or alkoxide. Specifically, for example, yttriumchloride, yttrium acetate, and yttrium nitrate may be used.

As required, the zirconia particles may be subjected to a surfacetreatment in advance with a known surface treatment agent selected from,for example, organic compounds having acidic groups; fatty acid amidessuch as saturated fatty acid amides, unsaturated fatty acid amides,saturated fatty acid bisamides, and unsaturated fatty acid bisamides;and organometallic compounds such as silane coupling agents(organosilicon compounds), organic titanium compounds, organic zirconiumcompounds, and organic aluminum compounds. A surface treatment ofzirconia particles allows for adjustments of miscibility with a liquidhaving a surface tension at 25° C. of 50 mN/m or less when such a liquidis contained in the dispersion medium of a slurry used when preparing azirconia particle- and fluorescent agent-containing powder, as will bedescribed later. A surface treatment also allows the zirconia particlesto have adjusted miscibility with a polymerizable monomer, for example,when producing the zirconia shaped body using a method that includespolymerizing a composition containing zirconia particles, a fluorescentagent, and a polymerizable monomer, as will be described later. Thesurface treatment agent is preferably an organic compound having anacidic group because of advantages such as desirable miscibility with aliquid having a surface tension at 25° C. of 50 mN/m or less, and theability to increase the strength of the resulting zirconia shaped bodyby improving the chemical bonding between the zirconia particles and apolymerizable monomer.

Examples of the organic compounds having acidic groups include organiccompounds having at least one acidic group, such as a phosphoric acidgroup, a carboxylic acid group, a pyrophosphoric acid group, athiophosphoric acid group, a phosphonic acid group, and a sulfonic acidgroup. Preferred are phosphoric acid group-containing organic compoundshaving at least one phosphoric acid group, and carboxylic acidgroup-containing organic compounds having at least one carboxylic acidgroup, of which the phosphoric acid group-containing organic compoundsare more preferred. The zirconia particles may be subjected to a surfacetreatment with one type of surface treatment agent, or with two or moretypes of surface treatment agents. In the case where the zirconiaparticles are subjected to a surface treatment with two or more types ofsurface treatment agents, the surface treatment layer produced may be asurface treatment layer of a mixture of two or more surface treatmentagents, or a surface treatment layer of a multilayer structure of aplurality of surface treatment layers.

Examples of the phosphoric acid group-containing organic compoundsinclude 2-ethylhexyl acid phosphate, stearyl acid phosphate,2-(meth)acryloyloxyethyl dihydrogen phosphate, 3-(meth)acryloyloxypropyldihydrogen phosphate, 4-(meth)acryloyloxybutyl dihydrogen phosphate,5-(meth)acryloyloxypentyl dihydrogen phosphate, 6-(meth)acryloyloxyhexyldihydrogen phosphate, 7-(meth)acryloyloxyheptyl dihydrogen phosphate,8-(meth)acryloyloxyoctyl dihydrogen phosphate, 9-(meth)acryloyloxynonyldihydrogen phosphate, 10-(meth)acryloyloxydecyl dihydrogen phosphate,11-(meth)acryloyloxyundecyl dihydrogen phosphate,12-(meth)acryloyloxydodecyl dihydrogen phosphate,16-(meth)acryloyloxyhexadecyl dihydrogen phosphate,20-(meth)acryloyloxyicosyl dihydrogen phosphate,bis[2-(meth)acryloyloxyethyl]hydrogen phosphate,bis[4-(meth)acryloyloxybutyl]hydrogen phosphate,bis[6-(meth)acryloyloxyhexyl]hydrogen phosphate,bis[8-(meth)acryloyloxyoctyl]hydrogen phosphate,bis[9-(meth)acryloyloxynonyl]hydrogen phosphate,bis[10-(meth)acryloyloxydecyl]hydrogen phosphate,1,3-di(meth)acryloyloxypropyl dihydrogen phosphate,2-(meth)acryloyloxyethylphenyl hydrogen phosphate,2-(meth)acryloyloxyethyl-2-bromoethyl hydrogen phosphate,bis[2-(meth)acryloyloxy-(1-hydroxymethyl)ethyl]hydrogen phosphate, andacid chlorides, alkali metal salts, and ammonium salts thereof.

Examples of the carboxylic acid group-containing organic compoundsinclude succinic acid, oxalic acid, octanoic acid, decanoic acid,stearic acid, polyacrylic acid, 4-methyloctanoic acid, neodecanoic acid,pivalic acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid,2,2-dimethylvaleric acid, 2,2-diethylbutyric acid, 3,3-diethylbutyricacid, naphthenic acid, cyclohexane dicarboxylic acid, (meth)acrylicacid, N-(meth)acryloylglycine, N-(meth)acryloylaspartic acid,O-(meth)acryloyltyrosine, N-(meth)acryloyltyrosine,N-(meth)acryloyl-p-aminobenzoic acid, N-(meth)acryloyl-o-aminobenzoicacid, p-vinyl benzoic acid, 2-(meth)acryloyloxybenzoic acid,3-(meth)acryloyloxybenzoic acid, 4-(meth)acryloyloxybenzoic acid,N-(meth)acryloyl-5-aminosalicylic acid,N-(meth)acryloyl-4-aminosalicylic acid, 2-(meth)acryloyloxyethylhydrogen succinate, 2-(meth)acryloyloxyethyl hydrogen phthalate,2-(meth)acryloyloxyethyl hydrogen maleate,2-(2-(2-methoxyethoxy)ethoxy)acetic acid (commonly known as “MEEAA”),2-(2-methoxyethoxy)acetic acid (commonly known as “MEAA”), succinic acidmono[2-(2-methoxyethoxy)ethyl]ester, maleic acidmono[2-(2-methoxyethoxy)ethyl]ester, glutaric acidmono[2-(2-methoxyethoxy)ethyl]ester, malonic acid, glutaric acid,6-(meth)acryloyloxyhexane-1,1-dicarboxylic acid,9-(meth)acryloyloxynonane-1,1-dicarboxylic acid,10-(meth)acryloyloxydecane-1,1-dicarboxylic acid,11-(meth)acryloyloxyundecane-1,1-dicarboxylic acid,12-(meth)acryloyloxydodecane-1,1-dicarboxylic acid,13-(meth)acryloyloxytridecane-1,1-dicarboxylic acid,4-(meth)acryloyloxyethyl trimellitate, 4-(meth)acryloyloxybutyltrimellitate, 4-(meth)acryloyloxyhexyl trimellitate,4-(meth)acryloyloxydecyl trimellitate,2-(meth)acryloyloxyethyl-3′-(meth)acryloyloxy-2′-(3,4-dicarboxybenzoyloxy)propylsuccinate,and acid anhydrides, acid halides, alkali metal salts, and ammoniumsalts thereof.

It is also possible to use organic compounds having at least one acidicgroup different from the acidic groups mentioned above (e.g., apyrophosphoric acid group, a thiophosphoric acid group, a phosphonicacid group, and a sulfonic acid group). For example, the organiccompounds mentioned in WO2012/042911 may be used as such organiccompounds.

Examples of the saturated fatty acid amides include palmitamide,stearamide, and behenamide. Examples of the unsaturated fatty acidamides include oleamide and erucamide. Examples of the saturated fattyacid bisamides include ethylene-bis-palmitamide,ethylene-bis-stearamide, and hexamethylene-bis-stearamide. Examples ofthe unsaturated fatty acid bisamides include ethylene-bis-oleamide,hexamethylene-bis-oleamide, and N,N′-dioleyl sebacamide.

Examples of the silane coupling agents (organosilicon compounds) includecompounds represented by R¹ _(n)SiX_(4-n) (wherein R¹ is a substitutedor unsubstituted hydrocarbon group of 1 to 12 carbon atoms, X is analkoxy group of 1 to 4 carbon atoms, a hydroxyl group, a halogen atom,or a hydrogen atom, and n is an integer of 0 to 3, and R¹ and X each maybe the same or different when a plurality of R¹ and X exists).

Specific examples of the silane coupling agents (organosiliconcompounds) include methyltrimethoxysilane, dimethyldimethoxysilane,phenyltrimethoxysilane, diphenyldimethoxysilane, methyltriethoxysilane,dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane,isobutyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane,vinyltris(β-methoxyethoxy)silane, 3,3,3-trifluoropropyltrimethoxysilane,methyl-3,3,3-trifluoropropyldimethoxysilane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane,γ-methacryloyloxypropylmethyldimethoxysilane,γ-methacryloyloxypropylmethyldiethoxysilane, N-(β-aminoethyl)γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, trimethylsilanol,methyltrichlorosilane, methyldichlorosilane, dimethyldichlorosilane,trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane,vinyltrichlorosilane, trimethylbromosilane, diethylsilane,vinyltriacetoxysilane, ω-(meth)acryloyloxyalkyltrimethoxysilane [3 to 12carbon atoms between the (meth)acryloyloxy group and the silicon atom,for example, such as in γ-methacryloyloxypropyltrimethoxysilane], andω-(meth)acryloyloxyalkyltriethoxysilane [3 to 12 carbon atoms betweenthe (meth)acryloyloxy group and the silicon atom, for example, such asin γ-methacryloyloxypropyltriethoxysilane]. As used herein, the notation“(meth)acryloyl” is meant to be inclusive of both methacryloyl andacryloyl.

Among these examples, silane coupling agents having functional groupsare preferred. Particularly preferred areω-(meth)acryloyloxyalkyltrimethoxysilane [3 to 12 carbon atoms betweenthe (meth)acryloyloxy group and the silicon atom],ω-(meth)acryloyloxyalkyltriethoxysilane [3 to 12 carbon atoms betweenthe (meth)acryloyloxy group and the silicon atom],vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, andγ-glycidoxypropyltrimethoxysilane.

Examples of the organic titanium compounds include tetramethyl titanate,tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimers,and tetra(2-ethylhexyl)titanate.

Examples of the organic zirconium compounds include zirconiumisopropoxide, zirconium n-butoxide, zirconium acetylacetonate, zirconylacetate.

Examples of the organic aluminum compounds include aluminumacetylacetonate, and aluminum organic acid salt chelate compounds.

The surface treatment method is not particularly limited, and may be aknown method, for example, such as a method the adds the surfacetreatment agent by spraying it while vigorously stirring the zirconiaparticles, or a method that disperses or dissolves the zirconiaparticles and the surface treatment agent in a suitable solvent, andremoves the solvent. The solvent may be a dispersion medium containing aliquid having a surface tension at 25° C. of 50 mN/m or less, as will bedescribed later. The zirconia particles and the surface treatment agentmay be subjected to a reflux or a high-temperature high-pressure process(e.g., autoclaving) after being dispersed or dissolved.

In producing a zirconia shaped body using the method having a shapingstep of shaping zirconia particles, the shaping step is not particularlylimited. However, for advantages such as ease of production of thezirconia shaped body of the present invention, and, in turn, thezirconia calcined body and the zirconia sintered body of the presentinvention, the shaping step is preferably any one of the followingsteps:

-   -   (i) a step of slip casting a slurry containing zirconia        particles and a fluorescent agent;    -   (ii) a step of gel casting a slurry containing zirconia        particles and a fluorescent agent;    -   (iii) a step of pressing a powder containing zirconia particles        and a fluorescent agent;    -   (iv) a step of shaping a composition containing zirconia        particles, a fluorescent agent, and a resin; and    -   (v) a step of polymerizing a composition containing zirconia        particles, a fluorescent agent, and a polymerizable monomer.

Slurry Containing Zirconia Particles and Fluorescent Agent

The method of preparation of a slurry containing zirconia particles anda fluorescent agent is not particularly limited, and the slurry may beobtained by, for example, mixing a zirconia particle-containing slurrywith a fluorescent agent. The zirconia particle-containing slurry may beone obtained after the breakdown or building-up process described above,or may be a commercially available product.

Preferably, a slurry containing zirconia particles and a fluorescentagent is prepared by mixing a zirconia particle-containing slurry with aliquid-state fluorescent agent because it enables the zirconia shapedbody and the zirconia calcined body of the present invention to beeasily obtained by preventing mixing of coarse particles, and therebyallows for easy production of the zirconia sintered body of the presentinvention that excels in both translucency and strength despitecontaining a fluorescent agent. The liquid-state fluorescent agent maybe, for example, a solution or a dispersion of a fluorescent agent,preferably a solution of a fluorescent agent. The solution is notparticularly limited, and may be, for example, an aqueous solution. Theaqueous solution may be, for example, a dilute nitric acid solution or adilute hydrochloric acid solution, and may be appropriately selectedaccording to conditions such as the type of the fluorescent agent used.

When producing a zirconia shaped body containing a colorant and/or atranslucency adjuster, and, in turn, a zirconia calcined body and azirconia sintered body containing a colorant and/or a translucencyadjuster, the colorant and/or translucency adjuster may be added to theslurry containing zirconia particles and a fluorescent agent. In thiscase, it is preferable that the colorant and/or translucency adjuster bemixed into the zirconia particle-containing slurry in a liquid form suchas a solution or a dispersion.

Powder Containing Zirconia Particles and Fluorescent Agent

The method of preparation of a powder containing zirconia particles anda fluorescent agent is not particularly limited, and the powder may beproduced by dry blending powdery zirconia particles with a powderyfluorescent agent (here, a colorant and/or a translucency adjuster alsomay be dry blended when adding a colorant and/or a translucency adjusterto the zirconia shaped body, and, in turn, to the zirconia calcined bodyand the zirconia sintered body). However, for advantages such asenabling production of a more homogenous zirconia sintered body ofimproved physical properties, it is preferable that the powder beobtained by drying the slurry containing zirconia particles and afluorescent agent. The slurry subjected to drying may additionallycontain a colorant and/or a translucency adjuster.

The drying method is not particularly limited, and may be, for example,spray drying, supercritical drying, freeze drying, hot-air drying, anddrying under reduced pressure. For advantages such as inhibitingparticle aggregation during the drying process and obtaining a morecompact zirconia sintered body, it is preferable to use any of spraydrying, supercritical drying, and freeze drying, more preferably spraydrying or supercritical drying, even more preferably spray drying.

The zirconia particle- and fluorescent agent-containing slurry to bedried may be a slurry containing water as dispersion medium. However,for advantages such as inhibiting particle aggregation during the dryingprocess and obtaining a more compact zirconia sintered body, the slurryis preferably a slurry containing a dispersion medium other than water,for example, such as an organic solvent.

Examples of the organic solvent include alcohols such as methanol,ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butylalcohol, 2-methoxyethanol, 2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol,diethylene glycol monobutyl ether, and glycerin; ketones such asacetone, and methyl ethyl ketone; ethers such as tetrahydrofuran,diethyl ether, diisopropyl ether, and 1,4-dioxane, and dimethoxyethane(including modified ethers such as propylene glycol monomethyl etheracetate (commonly known as “PGMEA”), preferably ether-modified ethersand/or ester-modified ethers, more preferably ether-modified alkyleneglycols and/or ester-modified alkylene glycols); esters such as ethylacetate and butyl acetate; hydrocarbons such as hexane and toluene; andhalogenated hydrocarbons such as chloroform and carbon tetrachloride.These organic solvents may be used alone, or two or more thereof may beused in combination. Considering safety against the body and ease ofremoval, the organic solvent is preferably a water-soluble organicsolvent. Specifically, the organic solvent is more preferably ethanol,2-propanol, tert-butyl alcohol, 2-ethoxyethanol,2-(2-ethoxyethoxy)ethanol, propylene glycol monomethyl ether acetate,acetone, or tetrahydrofuran.

When using spray drying in particular, it is preferable that thedispersion medium in the zirconia particle- and fluorescentagent-containing slurry to be dried contain a liquid having a surfacetension at 25° C. of 50 mN/m or less because it enables a more compactzirconia sintered body to be obtained by inhibiting particle aggregationduring the drying process. From this viewpoint, the surface tension ofthe liquid is preferably 40 mN/m or less, more preferably 30 mN/m orless.

The surface tension at 25° C. may be a value from, for example, theHandbook of Chemistry and Physics. For liquids that are not included inthis reference, the values recited in WO2014/126034 are usable. Thesurface tensions at 25° C. of liquids that are not included in either ofthese documents may be determined by using a known measurement method,for example, such as the ring method or the Wilhelmy method. Preferably,the surface tension at 25° C. is measured using the automatic surfacetensiometer CBVP-Z manufactured by Kyowa Interface Science Co., Ltd., orthe SIGMA702 manufactured by KSV Instruments Ltd.

The liquid may be an organic solvent having the foregoing ranges ofsurface tension. The organic solvent may be any of the organic solventsexemplified above and having the foregoing ranges of surface tension.However, for advantages such as inhibiting particle aggregation duringthe drying process and obtaining a more compact zirconia sintered body,the organic solvent is preferably at least one selected from the groupconsisting of methanol, ethanol, 2-methoxyethanol, 1,4-dioxane,2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol, more preferably at leastone selected from the group consisting of methanol, ethanol,2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol.

For advantages such as inhibiting particle aggregation during the dryingprocess and obtaining a more compact zirconia sintered body, the contentof the liquid in the dispersion medium is preferably 50 mass % or more,more preferably 80 mass % or more, even more preferably 95 mass % ormore, particularly preferably 99 mass % or more.

A slurry containing a dispersion medium other than water can be obtainedby replacing the dispersion medium in a slurry containing water asdispersion medium. The method used to replace the dispersion medium isnot particularly limited. For example, a method may be used that removeswater after adding a dispersion medium other than water (e.g., anorganic solvent) to a slurry containing water as dispersion medium. Inremoving water, part or all of the dispersion medium other than watermay be removed with water. The process of adding a dispersion mediumother than water and the subsequent removal of water may be repeatedmultiple times. Alternatively, a method may be used that precipitatesthe dispersoid after adding a dispersion medium other than water to aslurry containing water as dispersion medium. It is also possible toreplace the dispersion medium with a specific organic solvent in aslurry containing water as dispersion medium, followed by furtherreplacement with another organic solvent.

The fluorescent agent may be added after the replacement of dispersionmedium. However, for advantages such as obtaining a more homogenouszirconia sintered body of improved physical properties, the fluorescentagent is added preferably before the replacement of dispersion medium.Similarly, for advantages such as obtaining a more homogenous zirconiasintered body of improved physical properties, it is preferable to add acolorant and/or a translucency adjuster before the replacement ofdispersion medium when adding a colorant and/or a translucency adjusterto the slurry, though these may be added after the dispersion medium isreplaced.

The zirconia particle- and fluorescent agent-containing slurry to bedried may be subjected to a dispersion process that involves heat andpressure, for example, such as a reflux process or a hydrothermaltreatment. The zirconia particle- and fluorescent agent-containingslurry to be dried may be subjected to a mechanical dispersion processusing, for example, a roller mill, a colloid mill, a high-pressure spraydisperser, an ultrasonic disperser, a vibration mill, a planetary mill,or a bead mill. The slurry may be subjected to one of these processes,or two or more of these processes.

The zirconia particle- and fluorescent agent-containing slurry to bedried may contain one or more other components, for example, such as abinder, a plasticizer, a dispersant, an emulsifier, an antifoamingagent, a pH adjuster, and a lubricant. By containing such othercomponents (particularly, for example, a binder, a dispersant, and anantifoaming agent), it may be possible to inhibit particle aggregationduring the drying process, and obtain a more compact zirconia sinteredbody.

Examples of the binder include polyvinyl alcohol, methylcellulose,carboxymethylcellulose, acrylic binders, wax binders, polyvinyl butyral,polymethylmethacrylate, and ethylcellulose.

Examples of the plasticizer include polyethylene glycol, glycerin,propylene glycol, and dibutyl phthalic acid.

Examples of the dispersant include ammonium polycarboxylates (e.g.,triammonium citrate), ammonium polyacrylates, acryl copolymer resins,acrylic acid ester copolymers, polyacrylic acids, bentonite,carboxymethylcellulose, anionic surfactants (for example,polyoxyethylene alkyl ether phosphate esters such as polyoxyethylenelauryl ether phosphate ester), non-ionic surfactants, oleic glycerides,amine surfactants, and oligosugar alcohols.

Examples of the emulsifier include alkyl ethers, phenyl ether, sorbitanderivatives, and ammonium salts.

Examples of the antifoaming agent include alcohols, polyethers,polyethylene glycol, silicone, and waxes.

Examples of the pH adjuster include ammonia, ammonium salts (includingammonium hydroxides such as tetramethylammonium hydroxide), alkali metalsalts, and alkali-earth metal salts.

Examples of the lubricant include polyoxyethylene alkylate ether, andwaxes.

For advantages such as inhibiting particle aggregation during the dryingprocess and obtaining a more compact zirconia sintered body, themoisture content in the zirconia particle- and fluorescentagent-containing slurry to be dried is preferably 3 mass % or less, morepreferably 1 mass % or less, even more preferably 0.1 mass % or less.The moisture content may be measured with a Karl Fisher moisture contentmeter.

The drying conditions in the foregoing drying methods are notparticularly limited, and may be appropriately selected from knowndrying conditions. When using an organic solvent as dispersion medium,it is preferable that drying be carried out in the presence of anonflammable gas, more preferably in the presence of nitrogen, in orderto reduce the risk of explosion during the drying process.

In the case of supercritical drying, the supercritical fluid is notparticularly limited, and may be, for example, water or carbon dioxide.However, for advantages such as inhibiting particle aggregation andobtaining a more compact zirconia sintered body, the supercritical fluidis preferably carbon dioxide.

Composition Containing Zirconia Particles, Fluorescent Agent, and Resin

The method of preparation of a composition containing zirconiaparticles, a fluorescent agent, and a resin is not particularly limited,and the composition may be obtained by, for example, mixing the zirconiaparticle- and fluorescent agent-containing powder with a resin.

Composition Containing Zirconia Particles, Fluorescent Agent andPolymerizable Monomer

The method of preparation of a composition containing zirconiaparticles, a fluorescent agent, and a polymerizable monomer is notparticularly limited, and the composition may be obtained by, forexample, mixing the zirconia particle- and fluorescent agent-containingpowder with a polymerizable monomer.

(i) Slip Casting

In producing a zirconia shaped body by the method that includes a stepof slip casting a slurry containing zirconia particles and a fluorescentagent, the slip casting method is not particularly limited, and may be,for example, a method in which a slurry containing zirconia particlesand a fluorescent agent is dried after being poured into a mold.

For advantages such as ease of pouring into a mold, and increasing theusable lifetime of a mold by preventing long drying times, the contentof the dispersion medium in the zirconia particle- and fluorescentagent-containing slurry used is preferably 80 mass % or less, morepreferably 50 mass % or less, even more preferably 20 mass % or less.

The slurry may be poured into a mold under ordinary pressure. However,it is preferable for production efficiency that the slurry be pouredinto a mold under increased pressure conditions. The type of the moldused for slip casting is not particularly limited, and the mold may be,for example, a porous mold made of plaster, resin, ceramic, or the like.Resin molds and ceramic molds are desirable in terms of durability.

The zirconia particle- and fluorescent agent-containing slurry used forslip casting may additionally contain at least one of a colorant and atranslucency adjuster such as above, and may additionally contain one ormore other components, for example, such as the binders, plasticizers,dispersants, emulsifiers, antifoaming agents, pH adjusters, andlubricants exemplified above.

(ii) Gel Casting

In producing a zirconia shaped body by the method that includes a stepof gel casting a slurry containing zirconia particles and a fluorescentagent, the gel casting method is not particularly limited, and may be,for example, a method in which a zirconia particle- and fluorescentagent-containing slurry is shaped into a wet body by a process such asgelation, followed by drying.

For advantages such as preventing long drying times and inhibitingcracking during drying, the content of the dispersion medium in thezirconia particle- and fluorescent agent-containing slurry used ispreferably 80 mass % or less, more preferably 50 mass % or less, evenmore preferably 20 mass % or less.

The gelation may be initiated by addition of, for example, agelatinizer, or may be achieved by adding and polymerizing apolymerizable monomer. The type of the mold used is not particularlylimited, and the mold may be, for example, a porous mold made ofplaster, resin, ceramic, or the like, or a nonporous mold made of metal,resin, or the like.

The type of gelatinizer is not particularly limited, and, for example, awater-soluble gelatinizer may be used Specifically, for example, agaroseor gelatin may preferably be used. The gelatinizer may be one kind ofgelatinizer used alone, or may be two or more kinds of gelatinizers usedin combination. For considerations such as inhibiting cracking duringsintering, the gelatinizer content is preferably 10 mass % or less, morepreferably 5 mass % or less, even more preferably 1 mass % or lessrelative to the mass of the slurry after the gelatinizer is added.

The type of polymerizable monomer is not particularly limited. Examplesof the polymerizable monomer include 2-hydroxyethyl(meth)acrylate,3-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,6-hydroxyhexyl(meth)acrylate, 10-hydroxydecyl(meth)acrylate, propyleneglycol mono(meth)acrylate, glycerol mono(meth)acrylate, erythritolmono(meth)acrylate, N-methylol(meth)acrylamide,N-hydroxyethyl(meth)acrylamide, andN,N-(dihydroxyethyl)(meth)acrylamide. The polymerizable monomer may beused alone, or two or more thereof may be used in combination.

For considerations such as inhibiting cracking during sintering, thecontent of the polymerizable monomer is preferably 10 mass % or less,more preferably 5 mass % or less, even more preferably 1 mass % or lessrelative to the mass of the slurry after the polymerizable monomer isadded.

When gelation is achieved by polymerization of the polymerizablemonomer, the polymerization is carried out preferably with use of apolymerization initiator. The type of polymerization initiator is notparticularly limited. However, the polymerization initiator isparticularly preferably a photopolymerization initiator. Thephotopolymerization initiator may be appropriately selected fromphotopolymerization initiators commonly used in industry, preferablyfrom photopolymerization initiators used in dentistry.

Specific examples of the photopolymerization initiator include(bis)acylphosphine oxides (including salts), thioxanthones (includingsalts such as quaternary ammonium salts), ketals, α-diketones,coumarins, anthraquinones, benzoinalkyl ether compounds, andα-aminoketone compounds. The photopolymerization initiator may be usedalone, or two or more thereof may be used in combination. Among these,the photopolymerization initiator is preferably at least one selectedfrom the group consisting of (bis)acylphosphine oxides and α-diketones.In this way, polymerization (gelation) can be achieved both in theultraviolet region (including the near-ultraviolet region) and in thevisible light region. Specifically, polymerization (gelation) cansufficiently proceed regardless of whether the light source is a lasersuch as an Ar laser or a He—Cd laser; or a light such as a halogen lamp,a xenon lamp, a metal halide lamp, a light emitting diode (LED), amercury lamp, and a fluorescent lamp.

Examples of the acylphosphine oxides in the (bis)acylphosphine oxidesinclude 2,4,6-trimethylbenzoyldiphenylphosphine oxide (commonly known as“TPO”), 2,6-dimethoxybenzoyldiphenylphosphine oxide,2,6-dichlorobenzoyldiphenylphosphine oxide,2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide,2,4,6-trimethylbenzoylethoxyphenylphosphine oxide,2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide, benzoyldi-(2,6-dimethylphenyl)phosphonate, sodium salts of2,4,6-trimethylbenzoylphenylphosphine oxide, potassium salts of2,4,6-trimethylbenzoyldiphenylphosphine oxide, and ammonium salts of2,4,6-trimethylbenzoyldiphenylphosphine oxide.

Examples of the bisacylphosphine oxides in the (bis)acylphosphine oxidesinclude bis(2,6-dichlorobenzoyl)phenylphosphine oxide,bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide,bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide,bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide,bis(2,6-dimethoxybenzoyl)phenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, andbis(2,3,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide. It isalso possible to use other compounds, including, for example, thecompounds mentioned in JP-A-2000-159621.

Preferred among these (bis)acylphosphine oxides are2,4,6-trimethylbenzoyldiphenylphosphine oxide,2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and sodium salts of2,4,6-trimethylbenzoylphenylphosphine oxide.

Examples of the o-diketones include diacetyl, benzyl, camphorquinone,2,3-pentadione, 2,3-octadione, 9,10-phenanthrenequinone, 4,4′-oxybenzyl,and acenaphthenequinone. Preferred is camphorquinone, particularly whenusing a light source of the visible light region.

The zirconia particle- and fluorescent agent-containing slurry used forgel casting may additionally contain at least one of a colorant and atranslucency adjuster such as above, and may additionally contain one ormore other components, such as the binders, plasticizers, dispersants,emulsifiers, antifoaming agents, pH adjusters, and lubricantsexemplified above, as with the case of the slurry used for slip casting.

The method of drying the shaped wet body is not particularly limited,and may be, for example, natural drying, hot-air drying, vacuum drying,dielectric heating, induction heating, or constant-temperatureconstant-humidity drying. The drying may be achieved by using one ofthese methods, or two or more of these methods. For advantages such asinhibiting cracking during drying, the preferred drying methods arenatural drying, dielectric heating, induction heating, andconstant-temperature constant-humidity drying.

(iii) Pressing

In producing a zirconia shaped body by the method that includes a stepof pressing a powder containing zirconia particles and a fluorescentagent, the pressing is not particularly limited to specific methods, andmay be achieved by using a known pressing machine. Specific examples ofthe pressing method include uniaxial pressing. In order to increase thedensity of the zirconia shaped body produced, it is preferable thatuniaxial pressing be followed by cold isostatic pressing (CIP).

The zirconia particle- and fluorescent agent-containing powder used forpressing may additionally contain at least one of a colorant and atranslucency adjuster such as above, and may additionally contain one ormore other components, such as the binders, plasticizers, dispersants,emulsifiers, antifoaming agents, pH adjusters, and lubricantsexemplified above. These components may be added at the time ofpreparing the powder.

(iv) Shaping of Resin-Containing Composition

In producing a zirconia shaped body by the method that includes a stepof shaping a composition containing zirconia particles, a fluorescentagent, and a resin, the composition shaping method is not limited tospecific methods, and the composition may be shaped by using a method,for example, such as injection molding, cast molding, and extrusionmolding. It is also possible to shape the composition using a laminationshaping technique (e.g., 3D printing), for example, such as fuseddeposition modeling (FDM), an inkjet method, or a powder-binderlamination technique. Preferred as the shaping method are injectionmolding and cast molding, more preferably injection molding.

The resin is not limited to particular types of resins, and resins thatfunction as binders may preferably be used. Specific examples of theresin include fatty acids such as paraffin wax, polyvinyl alcohol,polyethylene, a polypropylene, ethylene-vinyl acetate copolymer,polystyrene, atactic polypropylene, (meth)acrylic resin, and stearicacid. These resins may be used alone, or two or more thereof may be usedin combination.

The composition containing zirconia particles, a fluorescent agent, anda resin may additionally contain at least one of a colorant and atranslucency adjuster such as above, and may additionally contain one ormore other components, such as the plasticizers, dispersants,emulsifiers, antifoaming agents, pH adjusters, and lubricantsexemplified above.

(v) Polymerization of Composition Containing Polymerizable Monomer

Polymerization of the composition containing zirconia particles, afluorescent agent, and a polymerizable monomer can polymerize thepolymerizable monomer in the composition, and cure the composition. Inproducing a zirconia shaped body by the method that includes apolymerization step, the method is not particularly limited to specificmethods, and may be, for example, (a) a method that polymerizes thezirconia particle-, fluorescent agent-, and polymerizablemonomer-containing composition in a mold; or (b) stereolithography (SLA)using the composition containing zirconia particles, a fluorescentagent, and a polymerizable monomer. Of these, (b) stereolithography ispreferred. By stereolithography, a shape corresponding to the shapedesired for the product zirconia sintered body can be imparted to thezirconia shaped body at the time of its production. This makes thestereolithography a potentially preferred method, particularly when thezirconia sintered body of the present invention is used as a dentalmaterial such as a dental prosthesis.

The type of the polymerizable monomer in the zirconia particle-,fluorescent agent-, and polymerizable monomer-containing composition isnot particularly limited, and the polymerizable monomer may be oneselected from monofunctional polymerizable monomers such asmonofunctional (meth)acrylates, and monofunctional (meth)acrylamides,and polyfunctional polymerizable monomers such as bifunctional aromaticcompounds, bifunctional aliphatic compounds, and tri and higherfunctional compounds. The polymerizable monomer may be used alone, ortwo or more thereof may be used in combination. Among these,polyfunctional polymerizable monomers are preferred, particularly whenstereolithography is used.

Examples of the monofunctional (meth)acrylates include (meth)acrylateshaving hydroxyl groups, such as 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate,10-hydroxydecyl(meth)acrylate, propylene glycol mono(meth)acrylate,glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate;alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate,sec-butyl(meth)acrylate, t-butyl(meth)acrylate, isobutyl(meth)acrylate,n-hexyl(meth)acrylate, lauryl(meth)acrylate, cetyl(meth)acrylate, andstearyl(meth)acrylate; alicyclic(meth)acrylates, such ascyclohexyl(meth)acrylate, and isobornyl(meth)acrylate; aromaticgroup-containing(meth)acrylates, such as benzyl(meth)acrylate, andphenyl(meth)acrylate; and (meth)acrylates having functional groups, suchas 2,3-dibromopropyl(meth)acrylate,3-(meth)acryloyloxypropyltrimethoxysilane, and11-(meth)acryloyloxyundecyltrimethoxysilane.

Examples of the monofunctional (meth)acrylamides include(meth)acrylamide, N-(meth)acryloylmorpholine,N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide,N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide,N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide,N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, andN,N-di(hydroxyethyl)(meth)acrylamide.

Among these monofunctional polymerizable monomers, (meth)acrylamides arepreferred, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide,and N,N-diethyl(meth)acrylamide are more preferred for their desirablepolymerizability.

Examples of the bifunctional aromatic compounds include2,2-bis((meth)acryloyloxyphenyl)propane,2,2-bis[4-(3-acryloyloxy-2-hydroxyprop oxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane (commonlyknown as “Bis-GMA”), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane,2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane,2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyditriethoxyphenyl)propane,2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)proane,2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate. Among these,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane (commonlyknown as “Bis-GMA”), and2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred fortheir desirable polymerizability and ability to provide desirablestrength for the zirconia shaped body produced. Preferred as2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane is2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (a compound with anaverage number of moles of ethoxy group added of 2.6; commonly known as“D-2.6E”).

Examples of the bifunctional aliphatic compounds include glyceroldi(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycoldi(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanedioldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 2-ethyl-1,6-hexanediol di(meth)acrylate,1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate,1,2-bis(3-methacryloyloxy-2-hydroxypropoxy)ethane, and2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl)dimethacrylate(commonly known as “UDMA”). Among these, triethylene glycoldimethacrylate (commonly known as “TEGDMA”), and2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl)dimethacrylate arepreferred for their desirable polymerizability and ability to providedesirable strength for the zirconia shaped body produced.

Examples of the tri and higher functional compounds includetrimethylolpropane tri(meth)acrylate, trimethylolethanetri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate,N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate, and1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxyheptane.Among these,N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate,and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxyheptane arepreferred for their desirable polymerizability and ability to providedesirable strength for the zirconia shaped body produced.

Regardless of whether the method (a) or (b) is used, it is preferablethat a polymerization initiator be used for the polymerization of thecomposition, and that the composition contain a polymerizationinitiator. The type of polymerization initiator is not particularlylimited, and the polymerization initiator is particularly preferably aphotopolymerization initiator. The photopolymerization initiator may beappropriately selected from photopolymerization initiators commonly usedin industry, preferably from photopolymerization initiators used indentistry. Specific examples of the photopolymerization initiatorinclude those exemplified above in conjunction with gel casting, and areomitted to avoid redundancy.

The composition containing zirconia particles, a fluorescent agent, anda polymerizable monomer may additionally contain at least one of acolorant and a translucency adjuster such as above, and may additionallycontain one or more other components, such as the plasticizers,dispersants, emulsifiers, antifoaming agents, pH adjusters, andlubricants exemplified above.

In producing a zirconia shaped body by stereolithography using thecomposition containing zirconia particles, a fluorescent agent, and apolymerizable monomer, the stereolithography is not particularly limitedto specific methods, and may be achieved by appropriately using a knownmethod. For example, the desired zirconia shaped body may be obtained byforming layers of desired shapes layer-by-layer throughphoto-polymerization of a liquid composition with, for example,ultraviolet light or a laser, using a stereolithography device.

In obtaining the zirconia shaped body by stereolithography, the contentof the zirconia particles in the zirconia particle-, fluorescent agent-,and polymerizable monomer-containing composition should preferably be ashigh as possible from the viewpoint of sinterability in a later step.Specifically, the zirconia particle content is preferably 20 mass % ormore, more preferably 30 mass % or more, even more preferably 40 mass %or more, particularly preferably 50 mass % or more. From the principleof layer formation in stereolithography, it is preferable that thecomposition have a viscosity that falls in a certain range. To this end,the content of the zirconia particles in the composition is preferably90 mass % or less, more preferably 80 mass % or less, even morepreferably 70 mass % or less, particularly preferably 60 mass % or less.Adjustment of composition viscosity may be of particular importance whenstereolithography is performed using the constrained surface method, inwhich light is applied upward through the bottom of a container to forma zirconia shaped body layer-by-layer, and when the composition needs tobe smoothly flown in between the bottom surface of the previously curedlayer and the bottom of the container for the formation of the nextlayer after the cured layer is elevated upward by the height of onelayer.

Specifically, the composition has a viscosity of preferably 20,000 mPa-sor less, more preferably 10,000 mPa-s or less, even more preferably5,000 mPa-s or less, and is preferably 100 mPa-s or more, in terms of aviscosity at 25° C. Because the viscosity of the composition tends toincrease with increase of the zirconia particle content, it ispreferable to appropriately adjust the balance between zirconia particlecontent and viscosity in the composition in a way suited for theperformance and other characteristics of the stereolithography device,taking into consideration factors such as the balance between the rateof the stereolithography process and the accuracy of the zirconia shapedbody produced. The viscosity may be measured with an E-type viscometer.

Zirconia Calcined Body

The zirconia calcined body of the present invention comprises afluorescent agent, and 4.5 to 9.0 mol % yttria, and has a three-pointflexural strength of 500 MPa or more after being sintered at 1,100° C.for 2 hours under ordinary pressure, and a crystal grain size of 180 nmor less after being sintered at 1,100° C. for 2 hours under ordinarypressure. The zirconia calcined body of the present invention may be aproduct obtained after the calcination of the zirconia shaped bodyformed from zirconia particles.

The fluorescent agent contained in the zirconia calcined body of thepresent invention may be the same fluorescent agent contained in thezirconia sintered body to be produced. The content of the fluorescentagent in the zirconia calcined body may be appropriately adjustedaccording to, for example, the content of the fluorescent agent in thezirconia sintered body to be produced. Specifically, the content of thefluorescent agent contained in the zirconia calcined body is preferably0.001 mass % or more, more preferably 0.005 mass % or more, even morepreferably 0.01 mass % or more, and is preferably 1 mass % or less, morepreferably 0.5 mass % or less, even more preferably 0.1 mass % or lessin terms of an oxide of the metallic element contained in thefluorescent agent, relative to the mass of the zirconia contained in thezirconia calcined body.

When producing a zirconia sintered body containing a colorant, it ispreferable that the colorant be contained in the zirconia calcined body.The colorant content in the zirconia calcined body may be appropriatelyadjusted according to, for example, the content of the colorant in thezirconia sintered body to be produced. Specifically, the colorantcontent in the zirconia calcined body is preferably 0.001 mass % ormore, more preferably 0.005 mass % or more, even more preferably 0.01mass % or more, and is preferably 5 mass % or less, more preferably 1mass % or less, even more preferably 0.5 mass % or less, and may be 0.1mass % or less, or 0.05 mass % or less in terms of an oxide of themetallic element contained in the colorant, relative to the mass of thezirconia contained in the zirconia calcined body.

When producing a zirconia sintered body containing a translucencyadjuster, it is preferable that the translucency adjuster be containedin the zirconia calcined body. The content of the translucency adjusterin the zirconia calcined body may be appropriately adjusted accordingto, for example, the content of the translucency adjuster in thezirconia sintered body to be produced. Specifically, the content of thetranslucency adjuster contained in the zirconia calcined body ispreferably 0.1 mass % or less relative to the mass of the zirconiacontained in the zirconia calcined body.

The yttria content in the zirconia calcined body of the presentinvention may be the same as that in the zirconia sintered body to beproduced. Specifically, the yttria content in the zirconia calcined bodyis 4.5 mol % or more, preferably 5.0 mol % or more, more preferably 5.5mol % or more, and is 9.0 mol % or less, preferably 8.0 mol % or less,more preferably 7.0 mol % or less. It is to be noted that the yttriacontent in the zirconia calcined body is a fraction (mol %) of thenumber of moles of yttria with respect to the total number of moles ofzirconia and yttria.

The density of the zirconia calcined body is not particularly limited,and preferably falls in a range of 3.0 to 6.0 g/m³, more preferably 3.2to 5.8 g/m³, though the density varies with conditions such as themethod of production of the zirconia shaped body used for the productionof the zirconia calcined body.

The shape of the zirconia calcined body is not particularly limited, andmay be chosen as desired according to use. However, for example,considering ease of handing of when using the zirconia calcined body asa mill blank for producing a dental material such as a dentalprosthesis, the zirconia calcined body preferably has a disc or a prismshape (e.g., rectangular). The zirconia calcined body may be cut(milled) into the desired shape according to use before being formedinto a zirconia sintered body, as will be described later. However, thepresent invention also encompasses zirconia calcined bodies of desiredshapes imparted after cutting (milling). The zirconia calcined body mayhave a monolayer structure or a multilayer structure. However, with amultilayered zirconia calcined body, the resulting zirconia sinteredbody can have a multilayer structure, which allows translucency andother physical properties to be locally altered.

For advantages such as maintaining the shape of the work in the processof working using a cutting machine, and improving the ease of cuttingitself, the three-point flexural strength of the zirconia calcined bodypreferably falls in a range of 10 to 70 MPa, more preferably 20 to 60MPa. The three-point flexural strength of the zirconia calcined body maybe a measured value obtained from a 5 mm×40 mm×10 mm test piece using amulti-purpose tester at a span length of 30 mm and a crosshead speed of0.5 mm/min.

The zirconia calcined body of the present invention has a crystal grainsize of 180 nm or less after being sintered at 1,100° C. for 2 hoursunder ordinary pressure (after being formed into a zirconia sinteredbody). In this way, the zirconia sintered body of the present inventionhaving excellent translucency can be produced with ease. For advantagessuch as obtaining a zirconia sintered body having even highertranslucency, the crystal grain size is preferably 140 nm or less, morepreferably 120 nm or less, even more preferably 115 nm or less, and maybe 110 nm or less. The lower limit of crystal grain size is notparticularly limited, and the crystal grain size may be, for example, 50nm or more, or 100 nm or more. The crystal grain size can be measured inthe same manner as in the crystal grain size measurement described abovein conjunction with the zirconia sintered body.

The zirconia calcined body of the present invention has a three-pointflexural strength of 500 MPa or more after being sintered at 1,100° C.for 2 hours under ordinary pressure (after being formed into a zirconiasintered body). In this way, the zirconia sintered body of the presentinvention having excellent strength can be produced with ease. Foradvantages such as obtaining a zirconia sintered body having even higherstrength, the three-point flexural strength is preferably 600 MPa ormore, more preferably 650 MPa or more, even more preferably 700 MPa ormore, particularly preferably 800 MPa or more. The upper limit ofthree-point flexural strength is not particularly limited, and thethree-point flexural strength may be, for example, 1,500 MPa or less, or1,000 MPa or less. The three-point flexural strength can be measured inthe same manner as in the measurement of three-point flexural strengthdescribed above in conjunction with the zirconia sintered body.

The zirconia calcined body has a transmittance of preferably 40% or morefor light of 700 nm wavelength through a thickness of 0.5 mm after beingsintered at 1,100° C. for 2 hours under ordinary pressure (after beingformed into a zirconia sintered body). In this way, the zirconiasintered body of the present invention having excellent translucency canbe produced with ease. For advantages such as obtaining a zirconiasintered body having even higher translucency, the transmittance is morepreferably 45% or more, and may be 46% or more, 48% or more, 50% ormore, or 52% or more. The upper limit of transmittance is notparticularly limited, and the transmittance may be, for example, 60% orless, or 57% or less. The transmittance can be measured in the samemanner as in the measurement of transmittance for light of 700 nmwavelength through a thickness of 0.5 mm described above in conjunctionwith the zirconia sintered body.

Method of Production of Zirconia Calcined Body

The zirconia calcined body of the present invention can be obtained bycalcining the zirconia shaped body. For advantages such as ease ofobtaining the desired zirconia calcined body, the calcinationtemperature is preferably 300° C. or more, more preferably 400° C. ormore, even more preferably 500° C. or more, and is preferably less than900° C., more preferably 850° C. or less, even more preferably 800° C.or less. With a calcination temperature equal to or greater than theforegoing lower limits, it is possible to effectively inhibit generationof organic material residues. With a calcination temperature equal to orless than the foregoing upper limits, it is possible to reduce thedifficulty in cutting (milling) with a cutting machine occurring whenthe sintering overly proceeds.

The rate of temperature increase in calcination is not particularlylimited, and is preferably 0.1° C./min or more, more preferably 0.2°C./min or more, even more preferably 0.5° C./min or more, and ispreferably 50° C./min or less, more preferably 30° C./min or less, evenmore preferably 20° C./min or less. The productivity improves when therate of temperature increase is equal to or greater than the foregoinglower limits. With a rate of temperature increase equal to or less thanthe foregoing upper limits, it is possible to reduce the volumedifference between inner and outer portions of the zirconia shaped bodyand the zirconia calcined body, and to reduce cracking and breakage byinhibiting the organic materials from undergoing rapid decompositionwhen the zirconia shaped body is containing organic materials.

The calcination time in the calcination of the zirconia shaped body isnot particularly limited. However, for advantages such as efficientlyand stably obtaining the desired zirconia calcined body with goodproductivity, the calcination time is preferably 0.5 hours or more, morepreferably 1 hour or more, even more preferably 2 hours or more, and ispreferably 10 hours or less, more preferably 8 hours or less, even morepreferably 6 hours or less.

Calcination may be carried out using a calcination furnace. The type ofcalcination furnace is not particularly limited, and the calcinationfurnace may be, for example, an electric furnace or a debinding furnacecommonly used in industry.

The zirconia calcined body may be cut (milled) into the desired shapeaccording to use, before being formed into a zirconia sintered body. Todescribe more specifically, the zirconia sintered body of the presentinvention excels in both translucency and strength despite containing afluorescent agent, and is particularly preferred as, for example, adental material such as a dental prosthesis. To this end, the zirconiacalcined body may be cut (milled) into a shape corresponding to theshape of such a material so that a zirconia sintered body for use insuch applications can be obtained. Cutting (milling) is not limited tospecific methods, and may be achieved by using, for example, a knownmilling device.

Method of Production of Zirconia Sintered Body

As described above, the zirconia sintered body of the present inventioncan be produced by sintering a zirconia shaped body containing afluorescent agent and 4.5 to 9.0 mol % yttria, under ordinary pressure.The zirconia sintered body of the present invention also can be producedby sintering a zirconia calcined body containing a fluorescent agent and4.5 to 9.0 mol % yttria under ordinary pressure.

For advantages such as ease of obtaining the desired zirconia sinteredbody, the sintering temperature is preferably 900° C. or more, morepreferably 1,000° C. or more, even more preferably 1,050° C. or more,and is preferably 1,200° C. or less, more preferably 1,150° C. or less,even more preferably 1,120° C. or less, regardless of whether thezirconia shaped body or the zirconia calcined body is sintered. With asintering temperature equal to or greater than the foregoing lowerlimits, sintering can sufficiently proceed, and a compact sintered bodycan be obtained with ease. With a sintering temperature equal to or lessthan the foregoing upper limits, it is possible to easily obtain azirconia sintered body having a crystal grain size within the ranges ofthe present invention, and to inhibit deactivation of fluorescent agent.

In sintering the zirconia shaped body and the zirconia calcined body,the sintering time is not particularly limited; however, for advantagessuch as efficiently and stably obtaining the desired zirconia sinteredbody with good productivity, the sintering time is preferably 5 minutesor more, more preferably 15 minutes or more, even more preferably 30minutes or more, and is preferably 6 hours or less, more preferably 4hours or less, even more preferably 2 hours or less, regardless ofwhether the zirconia shaped body or the zirconia calcined body issintered.

Sintering may be carried out using a sintering furnace. The type ofsintering furnace is not particularly limited, and the sintering furnacemay be, for example, an electric furnace or a debinding furnace commonlyused in industry. Specifically, when the zirconia sintered body is to beused for dental material applications, it is possible to use a dentalporcelain furnace, which operates in a relatively low sinteringtemperature range, other than using a traditional dental sinteringfurnace for zirconia.

The zirconia sintered body of the present invention can be produced withease without hot isostatic pressing (HIP). However, further improvementof translucency and strength can be achieved when the sintering underordinary pressure is followed by hot isostatic pressing (HIP).

Use of Zirconia Sintered Body

The zirconia sintered body of the present invention is not limited toparticular applications. However, because the zirconia sintered body ofthe present invention excels in both translucency and strength despitecontaining a fluorescent agent, the zirconia sintered body of thepresent invention is particularly preferred as a dental material such asa dental prosthesis, and is highly useful not only as a dentalprosthesis for the cervical region of a tooth, but as a dentalprosthesis for the occlusal surface of a posterior tooth, and theincisal region of a front tooth. The zirconia sintered body of thepresent invention is particularly preferred for use as a dentalprosthesis for the incisal region of a front tooth.

EXAMPLES

The following describes the present invention in greater detail usingExamples and Comparative Examples. It is to be noted, however, that thepresent invention is not limited by the following descriptions. Themethods used to measure physical properties are as follows.

(1) Average Primary Particle Diameter of Zirconia Particles

The average primary particle diameter of zirconia particles wasdetermined by taking a micrograph of zirconia particles with atransmission electron microscope (TEM), and finding a mean value ofparticle diameters (maximum diameters) measured for arbitrarily chosen100 particles from the photographed image.

(2) Crystal Grain Size

The crystal grain size of zirconia sintered body was determined bytaking a micrograph of zirconia sintered body cross sections with afield emission scanning electron microscope (FE-SEM), and finding a meanvalue of diameters of circles corresponding to 10 arbitrarily selectedparticles from the micrograph (the diameters of true circles having thesame areas as these particles).

(3) Three-Point Flexural Strength

The three-point flexural strength of zirconia sintered body was measuredin compliance with JIS R 1601:2008.

(4) Light Transmittance (700 nm Wavelength, 0.5 mm Thickness)

The transmittance of zirconia sintered body for light of 700 nmwavelength through a thickness of 0.5 mm was measured with anintegrating sphere by measuring light from a light source passing andscattering on a specimen, using a spectrophotometer (Hitachispectrophotometer, Model U-3900H manufactured by HitachiHigh-Technologies Corporation). In the measurement, the transmittancefor light of 700 nm wavelength was determined after measuringtransmittance in a wavelength region of 300 to 750 nm. For themeasurement, a disc-shaped zirconia sintered body having mirror polishedsurfaces and measuring 15 mm in diameter and 0.5 mm in thickness wasused as a specimen.

(5) Fraction of Cubical Crystal

The fraction of the cubical crystal in zirconia sintered body wasdetermined by crystal phase analysis. Specifically, the fraction ofcubical crystal was determined by X-ray diffraction (XRD) analysis of amirror finished surface portion of the zirconia sintered body, using thefollowing formula.

f _(c)=100×I _(c)(I _(m) +I _(t) +I _(c))

Here, f_(c) represents the fraction (%) of the cubical crystal inzirconia sintered body, I_(m) represents the height of a peak (a peakattributed to the (11-1) plane of a monocinic crystal) near 2θ=28degrees, I_(t) represents the height of a peak (a peak attributed to the(111) plane of a tetragonal crystal) near 2θ=30 degrees, and I_(c)represents the height of a peak (a peak attributed to the (111) plane ofthe cubical crystal) near 2θ=30 degrees.

(6) Fraction of Monoclinic Crystal after Hot-Water Treatment

The fraction of monoclinic crystal with respect to tetragonal crystaland cubical crystal after the zirconia sintered body is immersed in 180°C. hot water for 5 hours was determined by mirror polishing a surface ofthe zirconia sintered body, and measuring the mirror polished surfaceportion by X-ray diffraction (XRD) analysis after the zirconia sinteredbody was immersed in 180° C. hot water for 5 hours, using the followingformula.

f _(m)=100×I _(m)/(I _(t+c))

Here, f_(m) represents the fraction (%) of the monocinic crystal withrespect to the tetragonal crystal and the cubical crystal in thezirconia sintered body immersed in 180° C. hot water for 5 hours, I_(m)represents the height of a peak (a peak attributed to the (11-1) planeof the monoclinic crystal) near 2θ=28 degrees, and I_(t)+c representsthe height of a peak (a peak attributed to the mixed phase of the (111)plane of the tetragonal crystal and the (111) plane of the cubicalcrystal) near 2θ=30 degrees.

(7) Appearance of Zirconia Sintered Body

The appearance (color) of zirconia sintered body was evaluated by visualinspection.

(8) Fluorescence of Zirconia Sintered Body

For evaluation of the fluorescence of zirconia sintered body, thepresence or absence of fluorescence under UV light was determined byvisual inspection.

Example 1

A molding slurry containing zirconia particles and a fluorescent agentwas prepared by adding a dilute nitric acid solution of bismuth nitrateto a water-based zirconia slurry containing 5 mol % yttria (MELoxNanosize 5Y manufactured by MEL Chemicals; average primary particlediameter of zirconia particles=13 nm, zirconia concentration=23 mass %)so that the resulting mixture had a concentration of 0.02 mass % interms of an oxide of bismuth (Bi₂O₃) relative to the mass of zirconia.

The mixture was poured into a plaster mold, and allowed to stand for 2weeks at room temperature to obtain a zirconia shaped body. The plastermold was prepared by mixing water into a plaster (Noritake DentalPlaster manufactured by Kuraray Noritake Dental Inc.) in a proportion of50 mass %. The zirconia shaped body was calcined at 700° C. for 2 hoursunder ordinary pressure to obtain a zirconia calcined body. The zirconiacalcined body was then sintered at 1,100° C. for 2 hours under ordinarypressure to obtain a zirconia sintered body. The zirconia sintered bodyobtained was white in color, and had fluorescence. The measurementresults are presented in Table 1.

The zirconia calcined body produced in the manner described above wascut into shapes of crowns for maxillary central incisor and mandibularfirst molar using a milling device (Katana H-18 manufactured by KurarayNoritake Dental Inc.). These were then sintered at 1,100° C. for 2 hoursunder ordinary pressure to obtain crown-shaped dental prostheses havingfluorescence.

Example 2

A 1.0-L mixed aqueous solution of 0.62 mol/L zirconium oxychloride and0.066 mol/L yttrium chloride, and 0.5 L of a 1.9 mol/L aqueous solutionof sodium hydroxide were separately prepared.

After pouring 1.0 L of purified water into a precipitation vessel, themixed aqueous solution and the sodium hydroxide aqueous solution weresimultaneously poured into the vessel to obtain a slurry throughcoprecipitation of zirconium oxychloride and yttrium chloride. Theslurry was filtered and washed, and purified water was added to obtain a1.0-L slurry having a solid content of 5.0 mass % (a concentration ofzirconia and yttria). After adding 22.2 g of acetic acid to the slurry,a hydrothermal treatment was conducted at 200° C. for 3 hours to obtaina zirconia slurry. The zirconia particles contained in the zirconiaslurry had an average primary particle diameter of 17 nm.

A molding slurry, a zirconia shaped body, a zirconia calcined body, anda zirconia sintered body were obtained in the same manner as in Example1, except that the zirconia slurry prepared above was used. The zirconiasintered body obtained was white in color, and had fluorescence. Themeasurement results are presented in Table 1.

A zirconia calcined body produced in the same manner as described abovewas cut into shapes of crowns for maxillary central incisor andmandibular first molar using a milling device (Katana H-18 manufacturedby Kuraray Noritake Dental Inc.). These were then sintered at 1,100° C.for 2 hours under ordinary pressure to obtain crown-shaped dentalprostheses having fluorescence.

Example 3

A zirconia slurry was obtained in the same manner as in Example 2,except that a mixed aqueous solution of 0.62 mol/L zirconium oxychlorideand 0.072 mol/L yttrium chloride was used in place of the mixed aqueoussolution used in Example 2. The zirconia particles contained in thezirconia slurry had an average primary particle diameter of 17 nm.

A molding slurry, a zirconia shaped body, a zirconia calcined body, anda zirconia sintered body were obtained in the same manner as in Example1, except that the zirconia slurry prepared above was used. The zirconiasintered body obtained was white in color, and had fluorescence. Themeasurement results are presented in Table 1.

Example 4

A zirconia slurry was obtained in the same manner as in Example 2,except that a mixed aqueous solution of 0.62 mol/L zirconium oxychlorideand 0.093 mol/L yttrium chloride was used in place of the mixed aqueoussolution used in Example 2. The zirconia particles contained in thezirconia slurry had an average primary particle diameter of 18 nm.

A molding slurry, a zirconia shaped body, a zirconia calcined body, anda zirconia sintered body were obtained in the same manner as in Example1, except that the zirconia slurry prepared above was used. The zirconiasintered body obtained was white in color, and had fluorescence. Themeasurement results are presented in Table 1.

Example 5

A molding slurry, a zirconia shaped body, a zirconia calcined body, anda zirconia sintered body were obtained in the same manner as in Example1, except that a water-based zirconia slurry containing 8 mol % yttria(MELox Nanosize 8Y manufactured by MEL Chemicals; average primaryparticle diameter of zirconia particles=13 nm, zirconia concentration=23mass %) was used in place of the zirconia slurry used in Example 1. Thezirconia sintered body obtained was white in color, and hadfluorescence. The measurement results are presented in Table 1.

Comparative Example 1

A zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 1, exceptthat a water-based zirconia slurry containing 5 mol % yttria (MELoxNanosize 5Y manufactured by MEL Chemicals; average primary particlediameter of zirconia particles=13 nm, zirconia concentration=23 mass %)was directly used as a molding slurry. The zirconia sintered bodyobtained was white in color, but did not have fluorescence. Themeasurement results are presented in Table 1.

Comparative Example 2

A zirconia slurry was obtained in the same manner as in Example 2,except that a mixed aqueous solution of 0.62 mol/L zirconium oxychlorideand 0.130 mol/L yttrium chloride was used in place of the mixed aqueoussolution used in Example 2. The zirconia particles contained in thezirconia slurry had an average primary particle diameter of 18 nm.

A zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 1, exceptthat this zirconia slurry was directly used as a molding slurry. Thezirconia sintered body obtained was white in color, but did not havefluorescence. The measurement results are presented in Table 1.

Comparative Example 3

By uniaxial pressing, a zirconia particle powder TZ-8YS (manufactured byTosoh Corporation; average primary particle diameter=300 nm) was formedinto a plate shape measuring 80 mm×40 mm×10 mm in size, and a disc shapemeasuring 15 mm in diameter and 1.5 mm in thickness. These weresubjected to cold isostatic pressing (CIP; 170 MPa pressure) to obtainzirconia shaped bodies of increased density. These zirconia shapedbodies were calcined at 700° C. for 2 hours under ordinary pressure toobtain zirconia calcined bodies. The zirconia calcined bodies weresintered at 1,500° C. for 2 hours under ordinary pressure to obtainzirconia sintered bodies. The zirconia sintered bodies were white incolor, but did not have fluorescence. The measurement results arepresented in Table 1.

Comparative Example 4

A powder of bismuth nitrate was added to a water-based zirconia slurrycontaining 5 mol % yttria (MELox Nanosize 5Y manufactured by MELChemicals; average primary particle diameter of zirconia particles=13nm, zirconia concentration=23 mass %) so that the resulting mixture hada concentration of 0.02 mass % in terms of an oxide of bismuth (Bi₂O₃)relative to the mass of zirconia. The mixture was then pulverized with amortar to obtain a molding slurry containing zirconia particles and afluorescent agent.

A zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 1, exceptthat the slurry prepared above was used as a molding slurry. Thezirconia sintered body was white in color, and had fluorescence. Themeasurement results are presented in Table 1.

TABLE 1 Example Comparative Example Zirconia sintered body 1 2 3 4 5 1 23 4 Content of fluorescent agent (*1) Mass % 0.02 0.02 0.02 0.02 0.02 —— — 0.02 Content of colorant (*1) Mass % — — — — — — — — — Content ofyttria (*2) Mol % 5 5 5.5 7 8 5 9.5 8 5 Crystal grain size nm 108 119118 119 112 107 112 608 — Three-point flexural strength MPa 823 662 658642 650 838 480 350 488 Light transmittance (wavelength 700 % 50 46 4854 55 52 58 32 42 nm, thickness 0.5 mm) Fraction of cubical crystal %100 100 100 100 100 100 100 100 100 Fraction of monoclinic crystal after% 0 0 0 0 0 0 0 0 0 hot-water treatment (*1) Content relative to themass of zirconia (the content is in terms of an oxide of metallicelement) (*2) Fraction of number of moles of yttria with respect tototal number of moles of zirconia and yttria

Example 6

An aqueous solution of nickel(II) nitrate was added to a water-basedzirconia slurry containing 5 mol % yttria (MELox Nanosize 5Ymanufactured by MEL Chemicals; average primary particle diameter ofzirconia particles=13 nm, zirconia concentration=23 mass %) so that theresulting mixture had a concentration of 0.02 mass % in terms of anoxide of nickel(II) (NiO) relative to the mass of zirconia. A dilutenitric acid solution of bismuth nitrate was then added to the mixture sothat the resulting mixture had a concentration of 0.02 mass % in termsof an oxide of bismuth (Bi₂O₃) relative to the mass of zirconia. Thisproduced a molding slurry containing zirconia particles, a fluorescentagent, and a colorant. A zirconia shaped body, a zirconia calcined body,and a zirconia sintered body were obtained in the same manner as inExample 1, except that the slurry prepared above was used as a moldingslurry. The zirconia sintered body obtained was red in color, and hadfluorescence. The measurement results are presented in Table 2.

Example 7

A dilute nitric acid solution of bismuth nitrate was added to awater-based zirconia slurry containing 5 mol % yttria (MELox Nanosize 5Ymanufactured by MEL Chemicals; average primary particle diameter ofzirconia particles=13 nm, zirconia concentration=23 mass %) so that theresulting mixture had a concentration of 0.02 mass % in terms of anoxide of bismuth (Bi₂O₃) relative to the mass of zirconia. This wasfollowed by addition of tetramethylammonium hydroxide as a pH adjuster,and triammonium citrate as a dispersant. Thereafter, agarose was addedas a gelatinizer while stirring the mixture under heat to obtain amolding slurry containing zirconia particles, a fluorescent agent, a pHadjuster, a dispersant, and a gelatinizer.

The molding slurry was poured into a polypropylene mold, and dried atroom temperature for 16 days to obtain a zirconia shaped body. Thezirconia shaped body was calcined at 700° C. for 2 hours under ordinarypressure to obtain a zirconia calcined body. The zirconia calcined bodywas then sintered at 1,100° C. for 2 hours under ordinary pressure toobtain a zirconia sintered body. The zirconia sintered body obtained waswhite in color, and had fluorescence. The measurement results arepresented in Table 2.

Example 8

A dilute nitric acid solution of bismuth nitrate was added to 100 partsby mass of a water-based zirconia slurry containing 5 mol % yttria(MELox Nanosize 5Y manufactured by MEL Chemicals; average primaryparticle diameter of zirconia particles=13 nm, zirconia concentration=23mass %) so that the resulting mixture had a concentration of 0.02 mass %in terms of an oxide of bismuth (Bi₂O₃) relative to the mass ofzirconia. This was followed by a dispersion medium replacementprocedure, in which 50 parts by mass of 2-ethoxyethanol was added, andconcentrated to make the total amount 100 parts by mass, using a rotaryevaporator. The dispersion medium replacement procedure was repeated 4times to obtain a 2-ethoxyethanol-replaced slurry. The2-ethoxyethanol-replaced slurry had a residual moisture content of 0.05mass % as measured with a Karl Fisher moisture content meter.

The 2-ethoxyethanol-replaced slurry was dried with a spray drier (B-290manufactured by Buchi Labortechnik AG, Japan) at a feed rate of 5 mL/minand inlet and outlet temperatures of 150° C. and 100° C., respectively,to obtain a powder containing zirconia particles and a fluorescentagent.

By uniaxial pressing, the powder was formed into a plate shape measuring80 mm×40 mm×10 mm in size, and a disc shape measuring 15 mm in diameterand 1.5 mm in thickness. These were then subjected to cold isostaticpressing (CIP; 170 MPa pressure) to obtain zirconia shaped bodies ofincreased density. These zirconia shaped bodies were calcined at 700° C.for 2 hours under ordinary pressure to obtain zirconia calcined bodies.The zirconia calcined bodies were sintered at 1,100° C. for 2 hoursunder ordinary pressure to obtain zirconia sintered bodies. The zirconiasintered bodies obtained were white in color, and had fluorescence. Themeasurement results are presented in Table 2.

A zirconia calcined body produced in the same manner as described abovewas cut into shapes of crowns for maxillary central incisor andmandibular first molar using a milling device (Katana H-18 manufacturedby Kuraray Noritake Dental Inc.). These were then sintered at 1,100° C.for 2 hours under ordinary pressure to obtain crown-shaped dentalprostheses having fluorescence.

Example 9

Isopropanol was added to a water-based zirconia slurry containing 5 mol% yttria (MELox Nanosize 5Y manufactured by MEL Chemicals; averageprimary particle diameter of zirconia particles=13 nm, zirconiaconcentration=23 mass %) in 9 times the volume of the zirconia slurry.The mixture was placed in a centrifuge tube, thoroughly mixed, andcentrifuged at 4,000 rpm for 10 minutes. After confirming sedimentationof a white substance, the supernatant was removed, and isopropanol wasadded again. The mixture was thoroughly mixed, and centrifuged at 4,000rpm for 10 minutes. The supernatant was removed after confirmingsedimentation of a white substance, and methanol was added to make thevolume of the mixture the same as the volume of the zirconia slurryused. The mixture was then thoroughly mixed to obtain amethanol-replaced slurry. The methanol-replaced slurry had a residualmoisture content of 0.08 mass % as measured with a Karl Fisher moisturecontent meter.

A dilute nitric acid solution of bismuth nitrate was added to themethanol-replaced slurry so that the resulting mixture had aconcentration of 0.02 mass % in terms of an oxide of bismuth (Bi₂O₃)relative to the mass of zirconia. This produced a slurry containingzirconia particles and a fluorescent agent. The slurry was dried with aspray drier (B-290 manufactured by Buchi Labortechnik AG, Japan) at afeed rate of 5 mL/min and inlet and outlet temperatures of 150° C. and100° C., respectively, to obtain a powder containing zirconia particlesand a fluorescent agent.

A zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 8, exceptthat the powder produced above was used in place of the powder used inExample 8. The zirconia sintered body obtained was white in color, andhad fluorescence. The measurement results are presented in Table 2.

Example 10

An aqueous solution of bismuth hydroxide was added to 100 parts by massof a water-based zirconia slurry containing 8 mol % yttria (MELoxNanosize 8Y manufactured by MEL Chemicals; average primary particlediameter of zirconia particles=13 nm, zirconia concentration=23 mass %)so that the resulting mixture had a concentration of 0.02 mass % interms of an oxide of bismuth (Bi₂O₃) relative to the mass of zirconia.This was followed by a dispersion medium replacement procedure, in which50 parts by mass of 2-ethoxyethanol was added, and concentrated to makethe total amount 100 parts by mass, using a rotary evaporator. Thedispersion medium replacement procedure was repeated 4 times to obtain a2-ethoxyethanol-replaced slurry. The 2-ethoxyethanol-replaced slurry hada residual moisture content of 0.04 mass % as measured with a KarlFisher moisture content meter.

The 2-ethoxyethanol-replaced slurry was dried with a spray drier (B-290manufactured by Buchi Labortechnik AG, Japan) at a feed rate of 5 mL/minand inlet and outlet temperatures of 150° C. and 100° C., respectively,to obtain a powder containing zirconia particles and a fluorescentagent.

A zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 8, exceptthat the powder produced above was used in place of the powder used inExample 8. The zirconia sintered body obtained was white in color, andhad fluorescence. The measurement results are presented in Table 2.

Example 11

A dilute nitric acid solution of bismuth nitrate was added to awater-based zirconia slurry containing 5 mol % yttria (MELox Nanosize 5Ymanufactured by MEL Chemicals; average primary particle diameter ofzirconia particles=13 nm, zirconia concentration=23 mass %) so that theresulting mixture had a concentration of 0.02 mass % in terms of anoxide of bismuth (B₂O₃) relative to the mass of zirconia. Thereafter,isopropanol was added in 9 times the volume of the zirconia slurry used.The mixture was placed in a centrifuge tube, thoroughly mixed, andcentrifuged at 4,000 rpm for 10 minutes. After confirming sedimentationof a white substance, the supernatant was removed, and isopropanol wasadded again. The mixture was thoroughly mixed, and centrifuged at 4,000rpm for 10 minutes. The supernatant was removed after confirmingsedimentation of a white substance, and tert-butyl alcohol was added tomake the volume of the mixture the same as the volume of the zirconiaslurry used. The mixture was then thoroughly mixed to obtain atert-butyl alcohol-replaced slurry. The tert-butyl alcohol-replacedslurry had a residual moisture content of 0.05 mass % as measured with aKarl Fisher moisture content meter.

The tert-butyl alcohol-replaced slurry was transferred to an aluminumvat, and immersed in liquid nitrogen in a Dewar flask to freeze. Thefrozen tert-butyl alcohol-replaced slurry was allowed to stand in afreeze drier that had been precooled to −40° C. The pressure inside thefreeze drier was then reduced to 130 Pa or less with a vacuum pump tobring the temperature inside the freeze drier to −10° C. The internaltemperature was confirmed by inserting temperature sensors inside andoutside of the aluminum vat. After the temperature inside the freezedrier had stabilized at −10° C. for 72 hours, the temperature differenceinside and outside of the aluminum vat was confirmed to be within 5° C.,and the temperature inside the freeze drier was brought to 30° C. Afterbeing allowed to stand for 24 hours, the inside of the freeze drier wasreleased from the reduced pressure to obtain a powder containingzirconia particles and a fluorescent agent.

A zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 8, exceptthat the powder produced above was used in place of the powder used inExample 8. The zirconia sintered body obtained was white in color, andhad fluorescence. The measurement results are presented in Table 2.

TABLE 2 Example Zirconia sintered body 6 7 8 9 10 11 Content offluorescent agent(*l) Mass % 0.02 0.02 0.02 0.02 0.02 0.02 Content ofcolorant (*1) Mass % 0.02 — — — — — Content of yttria (*2) Mol % 5 5 5 58 5 Crystal grain size nm 119 108 114 115 114 111 Three-point flexuralstrength MPa 808 820 801 742 600 652 Light transmittance (wavelength 700nm, thickness 0.5 mm) % 47 50 46 42 51 41 Fraction of cubical crystal %100 100 100 100 100 100 Fraction of monoclinic crystal after hot-watertreatment % 0 0 0 0 0 0 (*1) Content relative to the mass of zirconia(the content is in terms of an oxide of metallic element) (*2) Fractionof number of moles of yttria with respect to total number of moles ofzirconia and yttria

Example 12

A dilute nitric acid solution of bismuth nitrate was added to awater-based zirconia slurry containing 5 mol % yttria (MELox Nanosize 5Ymanufactured by MEL Chemicals; average primary particle diameter ofzirconia particles=13 nm, zirconia concentration=23 mass %) so that theresulting mixture had a concentration of 0.02 mass % in terms of anoxide of bismuth (Bi₂O₃) relative to the mass of zirconia. Thereafter,isopropanol was added in 9 times the volume of the zirconia slurry used.The mixture was placed in a centrifuge tube, thoroughly mixed, andcentrifuged at 4,000 rpm for 10 minutes. After confirming sedimentationof a white substance, the supernatant was removed, and isopropanol wasadded again. The mixture was thoroughly mixed, and centrifuged at 4,000rpm for 10 minutes. The supernatant was removed after confirmingsedimentation of a white substance, and methanol was added to make thevolume of the mixture the same as the volume of the zirconia slurryused. The mixture was then thoroughly mixed to obtain amethanol-replaced slurry.

The methanol-replaced slurry produced was subjected to supercriticaldrying with a supercritical drier using the following procedure.Specifically, the methanol-replaced slurry was placed in a pressurevessel, and the pressure vessel was coupled to a supercritical carbondioxide extraction device. After checking that there is no pressureleak, the pressure vessel, with a preheating tube, was immersed in awater bath that had been heated to 60° C. The slurry was then allowed tostand for 10 minutes to stabilize after being heated to 80° C. andpressurized to 25 MPa. Thereafter, carbon dioxide and entrainer methanolwere introduced under predetermined conditions (temperature: 80° C.,pressure: 25 MPa, carbon dioxide flow rate: 10 mL/min, entrainer(methanol) flow rate: 1.5 mL/min). The feeding of methanol wasdiscontinued after an elapsed time period of 2 hours, without stoppingthe carbon dioxide feed. After 2 hours with the sole supply of carbondioxide, the feeding of carbon dioxide was stopped, and the pressure wasgradually brought back to ordinary pressure from 25 MPa over a timeperiod of about 20 minutes at a maintained temperature of 80° C. Thepressure vessel was then taken out of the water bath, and cooled toordinary temperature. The processed specimen was collected by openingthe container, and a powder containing zirconia particles and afluorescent agent was obtained.

A zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 8, exceptthat the powder produced above was used in place of the powder used inExample 8. The zirconia sintered body obtained was white in color, andhad fluorescence. The measurement results are presented in Table 3.

Example 13

A 1.0-L mixed aqueous solution of 0.62 mol/L zirconium oxychloride and0.065 mol/L yttrium chloride, and 0.5 L of a 1.9 mol/L aqueous solutionof sodium hydroxide were separately prepared.

After pouring 1.0 L of purified water into a precipitation vessel, themixed aqueous solution and the sodium hydroxide aqueous solution weresimultaneously poured into the vessel to obtain a slurry throughcoprecipitation of zirconium oxychloride and yttrium chloride. Theslurry was filtered and washed, and purified water was added to obtain a1.0-L slurry having a solid content of 5.0 mass % (a concentration ofzirconia and yttria). After adding 22.2 g of acetic acid to the slurry,a hydrothermal treatment was conducted at 200° C. for 3 hours to obtaina zirconia slurry. The zirconia particles contained in the zirconiaslurry had an average primary particle diameter of 18 nm.

A dilute nitric acid solution of bismuth nitrate was added to 100 partsby mass of the zirconia slurry so that the resulting mixture had aconcentration of 0.02 mass % in terms of an oxide of bismuth (Bi₂O₃)relative to the mass of zirconia. This was followed by a dispersionmedium replacement procedure, in which 50 parts by mass of2-ethoxyethanol was added, and concentrated to make the total amount 100parts by mass, using a rotary evaporator. The dispersion mediumreplacement procedure was repeated 4 times to obtain a2-ethoxyethanol-replaced slurry. The 2-ethoxyethanol-replaced slurry hada residual moisture content of 0.06 mass % as measured with a KarlFisher moisture content meter.

A zirconia particle- and fluorescent agent-containing powder, a zirconiashaped body, a zirconia calcined body, and a zirconia sintered body wereobtained in the same manner as in Example 12, except that the2-ethoxyethanol-replaced slurry produced above was used in place of themethanol-replaced slurry. The zirconia sintered body obtained was whitein color, and had fluorescence. The measurement results are presented inTable 3.

Example 14

An aqueous solution of nickel(II) nitrate was added to 100 parts by massof a water-based zirconia slurry containing 5 mol % yttria (MELoxNanosize 5Y manufactured by MEL Chemicals; average primary particlediameter of zirconia particles=13 nm, zirconia concentration=23 mass %)so that the resulting mixture had a concentration of 0.02 mass % interms of an oxide of nickel(II) (NiO) relative to the mass of zirconia.A dilute nitric acid solution of bismuth nitrate was then added to themixture so that the resulting mixture had a concentration of 0.02 mass %in terms of an oxide of bismuth (Bi₂O₃) relative to the mass ofzirconia. This was followed by a dispersion medium replacementprocedure, in which 50 parts by mass of 2-ethoxyethanol was added,concentrated to make the total amount 100 parts by mass, using a rotaryevaporator. The dispersion medium replacement procedure was repeated 4times to obtain a 2-ethoxyethanol-replaced slurry. The2-ethoxyethanol-replaced slurry had a residual moisture content of 0.02mass % as measured with a Karl Fisher moisture content meter.

A zirconia particle-, fluorescent agent-, and colorant-containingpowder, a zirconia shaped body, a zirconia calcined body, and a zirconiasintered body were obtained in the same manner as in Example 12, exceptthat the 2-ethoxyethanol-replaced slurry produced above was used inplace of the methanol-replaced slurry. The zirconia sintered bodyobtained was red in color, and had fluorescence. The measurement resultsare presented in Table 3.

Example 15

An aqueous solution of europium acetate was added to a water-basedzirconia slurry containing 5 mol % yttria (MELox Nanosize 5Ymanufactured by MEL Chemicals; average primary particle diameter ofzirconia particles=13 nm, zirconia concentration=23 mass %) so that theresulting mixture had a concentration of 0.02 mass % in terms of anoxide of europium (Eu₂O₃) relative to the mass of zirconia. Thereafter,isopropanol was added in 9 times the volume of the zirconia slurry used.The mixture was placed in a centrifuge tube, thoroughly mixed, andcentrifuged at 4,000 rpm for 10 minutes. After confirming sedimentationof a white substance, the supernatant was removed, and isopropanol wasadded again. The mixture was thoroughly mixed, and centrifuged at 4,000rpm for 10 minutes. The supernatant was removed after confirmingsedimentation of a white substance, and methanol was added to make thevolume of the mixture the same as the volume of the zirconia slurryused. The mixture was then thoroughly mixed to obtain amethanol-replaced slurry. The methanol-replaced slurry had a residualmoisture content of 0.08 mass % as measured with a Karl Fisher moisturecontent meter.

A zirconia particle- and fluorescent agent-containing powder, a zirconiashaped body, a zirconia calcined body, and a zirconia sintered body wereobtained in the same manner as in Example 12, except that themethanol-replaced slurry produced above was used in place of themethanol-replaced slurry used in Example 12. The zirconia sintered bodyobtained was white in color, and had fluorescence. The measurementresults are presented in Table 3.

A zirconia calcined body produced in the same manner as described abovewas cut into shapes of crowns for maxillary central incisor andmandibular first molar using a milling device (Katana H-18 manufacturedby Kuraray Noritake Dental Inc.). These were then sintered at 1,100° C.for 2 hours under ordinary pressure to obtain crown-shaped dentalprostheses having fluorescence.

Example 16

A composition containing zirconia particles, a fluorescent agent, and aresin was obtained by adding and kneading 30 parts by mass of polyvinylalcohol into 50 parts by mass of a zirconia particle- and fluorescentagent-containing powder obtained in the same manner as in Example 12.

The composition was formed into a zirconia shaped body by injectionmolding using an injection molding machine. The zirconia shaped body wascalcined at 700° C. for 2 hours under ordinary pressure to obtain azirconia calcined body. The zirconia calcined body was sintered at1,100° C. for 2 hours under ordinary pressure to obtain a zirconiasintered body. The zirconia sintered body obtained was white in color,and had fluorescence. The measurement results are presented in Table 3.

Example 17

In a dark room, 30 parts by mass of 2-hydroxyethylmethacrylate, 5 partsby mass of 10-methacryloyloxydecyl dihydrogen phosphate, and 1 part bymass of 2,4,6-trimethylbenzoyldiphenylphosphine oxide(photopolymerization initiator) were added and kneaded into 50 parts bymass of a zirconia particle- and fluorescent agent-containing powderobtained in the same manner as in Example 12. This produced acomposition containing zirconia particles, a fluorescent agent, apolymerizable monomer, and a photopolymerization initiator.

The composition was charged into a mold, and polymerized with a UVirradiator to obtain a zirconia shaped body. The zirconia shaped bodywas calcined at 700° C. for 2 hours under ordinary pressure to obtain azirconia calcined body. The zirconia calcined body was sintered at1,100° C. for 2 hours under ordinary pressure to obtain a zirconiasintered body. The zirconia sintered body obtained was white in color,and had fluorescence. The measurement results are presented in Table 3.

Example 18

(1) Eighty parts by mass of propylene glycol monomethyl ether acetate(commonly known as “PGMEA”) as organic solvent, and six parts by mass of2-(2-(2-methoxyethoxy)ethoxy)acetic acid (commonly known as “MEEAA”) assurface treatment agent were added to 100 parts by mass of a water-basedzirconia slurry containing 5 mol % yttria (MELox Nanosize 5Ymanufactured by MEL Chemicals; average primary particle diameter ofzirconia particles=13 nm, zirconia concentration=23 mass %). The mixturewas transferred to a round-bottom flask, and about 60 parts by mass ofwater and PGMEA was removed under reduced pressure, using a rotaryevaporator. After adding toluene to the residue, the same removalprocedure was carried out under reduced pressure to remove water, PGMEA,and toluene in the form of an azeotrope. The azeotrope removal procedureby addition of toluene to the residue was repeated several times tothoroughly remove water, and a transparent, fluidic slurry containing 45mass % zirconia particles was obtained. The main component of thedispersion medium in the slurry is PGMEA.

(2) To 20 parts by mass of the slurry obtained above were added 4 partsby mass of triethylene glycol dimethacrylate (commonly known as“TEGDMA”), 4 parts by mass of 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl)dimethacrylate [a substance obtained afteradding 2-hydroxyethylmethacrylate to2,2,4-trimethylhexamethylenediisocyanate in a molar ratio of 2:1;commonly known as “UDMA” ], and 0.6 parts by mass of2,4,6-trimethylbenzoyldiphenylphosphine oxide (commonly known as “TPO”;a photopolymerization initiator). These were uniformly mixed anddissolved. A dilute hydrochloric acid solution of bismuth acetate oxideas fluorescent agent was then mixed into the mixture so that theresulting mixture had a concentration of 0.01 mass % in terms of anoxide of bismuth (Bi₂O₃) relative to the mass of zirconia. This produceda composition containing zirconia particles, a fluorescent agent, apolymerizable monomer, and a photopolymerization initiator. Thecomposition had a viscosity at 25° C. of 2,500 mPa-s (as measured withan E-type viscometer).

(3) The composition was poured into a polytetrafluoroethylene mold(measuring 3 cm×3 cm in size with a depth of 5 mm), and polymerized andcured under light applied for 5 minutes with a dentalphoto-polymerization irradiator (α-Light III manufactured by Morita Mfg.Corp.). The cured product was allowed to stand at room temperature inair for 3 days to dry, and released from the mold to obtain a zirconiashaped body.

(4) The zirconia shaped body produced was calcined under ordinarypressure to obtain a zirconia calcined body, using an electric furnace(Katana F manufactured by Kuraray Noritake Dental Inc.). The calcinationwas conducted by increasing temperature from room temperature to 200° C.at a rate of 0.3° C./min, 200° C. to 260° C. at a rate of 0.1° C./min,and 260° C. to 400° C. at a rate of 0.3° C./min. The zirconia calcinedbody was then put back in the electric furnace, and was sintered byincreasing temperature to 1,050° C. at a rate of 60° C./hour underordinary pressure to obtain a compact zirconia sintered body. Thezirconia sintered body obtained was white in color, and hadfluorescence. The measurement results are presented in Table 3.

TABLE 3 Example Zirconia sintered body 12 13 14 15 16 17 18 Content offluorescent agent(*l) Mass % 0.02 0.02 0.02 0.02 0.02 0.02 0.01 Contentof colorant (*1) Mass % — — 0.02 — — — — Content of yttria (*2) Mol % 55 5 5 5 5 5 crystal grain size nm 110 118 119 112 118 118 118Three-point flexural strength MPa 802 636 802 802 720 692 750 Lighttransmittance (wavelength 700 nm, thickness 0.5 mm) % 48 42 43 46 46 4647 Fraction of cubical crystal % 100 100 100 100 100 100 — Fraction ofmonoclinic crystal after hot-water treatment % 0 0 0 0 0 0 — (*1)Content relative to the mass of zirconia (the content is in terms of anoxide of metallic element) (*2) Fraction of number of moles of yttriawith respect to total number of moles of zirconia and yttria

1: A zirconia sintered body comprising a fluorescent agent, wherein thezirconia sintered body comprises 4.5 to 9.0 mol % yttria, and has acrystal grain size of 180 nm or less, and a three-point flexuralstrength of 500 MPa or more. 2: The zirconia sintered body according toclaim 1, wherein the fluorescent agent contains a metallic element, andthe zirconia sintered body comprises the fluorescent agent in an amountof 0.001 to 1 mass % in terms of an oxide of the metallic elementrelative to a mass of zirconia. 3: The zirconia sintered body accordingto claim 1, wherein the zirconia sintered body has a transmittance of40% or more for light of 700 nm wavelength through a thickness of 0.5mm. 4: The zirconia sintered body according to claim 1, wherein thezirconia sintered body comprises a cubical crystal as a predominantcrystal phase. 5-7. (canceled) 8: A zirconia shaped body comprising afluorescent agent, wherein the zirconia shaped body comprises 4.5 to 9.0mol % yttria, and has a three-point flexural strength of 500 MPa or moreafter being sintered at 1,100° C. for 2 hours under ordinary pressure,and a crystal grain size of 180 nm or less after being sintered at1,100° C. for 2 hours under ordinary pressure.
 9. (canceled) 10: Thezirconia shaped body according to claim 8, wherein the fluorescent agentcomprises a metallic element, and the zirconia shaped body comprises thefluorescent agent in an amount of 0.001 to 1 mass % in terms of an oxideof the metallic element relative to a mass of zirconia. 11: The zirconiashaped body according to claim 8, wherein the zirconia shaped body has atransmittance of 40% or more for light of 700 nm wavelength through athickness of 0.5 mm after being sintered at 1,100° C. for 2 hours underordinary pressure. 12: A zirconia calcined body comprising a fluorescentagent, wherein the zirconia calcined body comprises 4.5 to 9.0 mol %yttria, and has a three-point flexural strength of 500 MPa or more afterbeing sintered at 1,100° C. for 2 hours under ordinary pressure, and acrystal grain size of 180 nm or less after being sintered at 1,100° C.for 2 hours under ordinary pressure.
 13. (canceled) 14: The zirconiacalcined body according to claim 12, wherein the fluorescent agentcontains a metallic element, and the zirconia calcined body comprisesthe fluorescent agent in an amount of 0.001 to 1 mass % in terms of anoxide of the metallic element relative to a mass of zirconia. 15: Thezirconia calcined body according to claim 12, wherein the zirconiacalcined body has a transmittance of 40% or more for light of 700 nmwavelength through a thickness of 0.5 mm after being sintered at 1,100°C. for 2 hours under ordinary pressure. 16: A method for producing thezirconia shaped body of claim 8, comprising a shaping step of shapingzirconia particles, wherein the zirconia particles comprise 4.5 to 9.0mol % yttria, and have an average primary particle diameter of 20 nm orless.
 17. (canceled) 18: The method according to claim 16, wherein theshaping step is a step of slip casting a slurry comprising zirconiaparticles and a fluorescent agent. 19: The method according to claim 16,wherein the shaping step is a step of gel casting a slurry comprisingzirconia particles and a fluorescent agent. 20: The method according toclaim 16, wherein the shaping step is a step of pressing a powdercomprising zirconia particles and a fluorescent agent. 21: The methodaccording to claim 16, wherein the shaping step is a step of shaping acomposition comprising zirconia particles, a fluorescent agent, and aresin.
 22. (canceled) 23: The method according to claim 21, wherein theshaping step is a stereolithography process. 24: A method for producingthe zirconia calcined body of claim 12, comprising a step of calcining azirconia shaped body, wherein the zirconia shaped body comprises afluorescent agent, and wherein the zirconia shaped body comprises 4.5 to9.0 mol % yttria, and has a three-point flexural strength of 500 MPa ormore after being sintered at 1,100° C. for 2 hours under ordinarypressure, and a crystal grain size of 180 nm or less after beingsintered at 1,100° C. for 2 hours under ordinary pressure. 25: Themethod according to claim 24, wherein the calcination is carried outbetween 300° C. or more and less than 900° C. 26: A method for producingthe zirconia sintered body of claim 1, comprising a step of sintering azirconia shaped body under ordinary pressure, wherein the zirconiashaped body comprises a fluorescent agent, and wherein the zirconiashaped body comprises 4.5 to 9.0 mol % yttria, and has a three-pointflexural strength of 500 MPa or more after being sintered at 1,100° C.for 2 hours under ordinary pressure, and a crystal grain size of 180 nmor less after being sintered at 1,100° C. for 2 hours under ordinarypressure.
 27. (canceled) 28: A method for producing the zirconiasintered body of claim 1, comprising sintering a zirconia calcined bodyunder ordinary pressure, wherein the zirconia sintered body comprises afluorescent agent, and wherein the zirconia sintered body comprises 4.5to 9.0 mol % yttria, and has a crystal grain size of 180 nm or less, anda three-point flexural strength of 500 MPa or more.
 29. (canceled)